diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index 584feb7c53..91d7695006 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -303,4 +303,28 @@ public function getOriginal($key = '', $apply_overrides = TRUE) {
     }
   }
 
+  /**
+   * Determines if overrides are applied to a key for this configuration object.
+   *
+   * @param string $key
+   *   A string that maps to a key within the configuration data.
+   *
+   * @return bool
+   *   TRUE if there are any overrides for the key, otherwise FALSE.
+   */
+  public function hasOverrides($key = '') {
+    if ($key) {
+      $parts = explode('.', $key);
+      $override_exists = FALSE;
+      if (isset($this->moduleOverrides) && is_array($this->moduleOverrides)) {
+        $override_exists = NestedArray::keyExists($this->moduleOverrides, $parts);
+      }
+      if (!$override_exists && isset($this->settingsOverrides) && is_array($this->settingsOverrides)) {
+        $override_exists = NestedArray::keyExists($this->settingsOverrides, $parts);
+      }
+      return $override_exists;
+    }
+    return !empty($this->moduleOverrides) || !empty($this->settingsOverrides);
+  }
+
 }
diff --git a/core/modules/settings_tray/settings_tray.module b/core/modules/settings_tray/settings_tray.module
index af04450459..d73ca617bf 100644
--- a/core/modules/settings_tray/settings_tray.module
+++ b/core/modules/settings_tray/settings_tray.module
@@ -10,6 +10,8 @@
 use Drupal\settings_tray\Block\BlockEntityOffCanvasForm;
 use Drupal\settings_tray\Form\SystemBrandingOffCanvasForm;
 use Drupal\settings_tray\Form\SystemMenuOffCanvasForm;
+use Drupal\block\BlockInterface;
+use Drupal\block\Entity\Block;
 
 /**
  * Implements hook_help().
@@ -48,6 +50,21 @@ function settings_tray_contextual_links_view_alter(&$element, $items) {
   }
 }
 
+/**
+ * Checks if a block has overrides.
+ *
+ * @param \Drupal\block\BlockInterface $block
+ *   The block to check for overrides.
+ *
+ * @return bool
+ *   TRUE if the block has overrides otherwise FALSE.
+ *
+ * @internal
+ */
+function _settings_tray_has_block_overrides(BlockInterface $block) {
+  return \Drupal::config($block->getEntityType()->getConfigPrefix() . '.' . $block->id())->hasOverrides();
+}
+
 /**
  * Implements hook_block_view_alter().
  */
@@ -190,3 +207,15 @@ function settings_tray_css_alter(&$css, AttachedAssetsInterface $assets) {
     $css[$path]['group'] = 200;
   }
 }
+
+/**
+ * Implements hook_contextual_links_alter().
+ */
+function settings_tray_contextual_links_alter(array &$links, $group, array $route_parameters) {
+  if (isset($links['settings_tray.block_configure']['route_parameters']['block'])) {
+    $block = Block::load($links['settings_tray.block_configure']['route_parameters']['block']);
+    if (_settings_tray_has_block_overrides($block)) {
+      $links['settings_tray.block_configure']['route_name'] = 'settings_tray.overridden_block_warning';
+    }
+  }
+}
diff --git a/core/modules/settings_tray/settings_tray.routing.yml b/core/modules/settings_tray/settings_tray.routing.yml
index 01109e4c79..c2f4f7c140 100644
--- a/core/modules/settings_tray/settings_tray.routing.yml
+++ b/core/modules/settings_tray/settings_tray.routing.yml
@@ -6,3 +6,10 @@ entity.block.off_canvas_form:
   requirements:
     _permission: 'administer blocks'
     _access_block_plugin_has_settings_tray_form: 'TRUE'
+settings_tray.overridden_block_warning:
+  path: '/admin/settings-tray-overridden/{block}'
+  defaults:
+    _controller: '\Drupal\settings_tray\Controller\OverriddenBlockConfig::overrideNotice'
+    _title_callback: '\Drupal\settings_tray\Block\BlockEntityOffCanvasForm::title'
+  requirements:
+    _permission: 'administer blocks'
diff --git a/core/modules/settings_tray/src/Controller/OverriddenBlockConfig.php b/core/modules/settings_tray/src/Controller/OverriddenBlockConfig.php
new file mode 100644
index 0000000000..50efd38d7c
--- /dev/null
+++ b/core/modules/settings_tray/src/Controller/OverriddenBlockConfig.php
@@ -0,0 +1,48 @@
+<?php
+
+namespace Drupal\settings_tray\Controller;
+
+use Drupal\block\BlockInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\Url;
+
+/**
+ * Controller to display overridden block notice and edit link.
+ *
+ * Overridden blocks cannot be overridden in Settings Tray functionality
+ * because there is no uniform method for editing any potential configuration
+ * override.
+ *
+ * @see settings_tray_block_view_alter()
+ */
+class OverriddenBlockConfig {
+
+  use StringTranslationTrait;
+
+  /**
+   * Provides a notice for overridden blocks and a link to edit them.
+   *
+   * @param \Drupal\block\BlockInterface $block
+   *   The block that is overridden.
+   *
+   * @return array
+   *   The render array for the notice and block edit link.
+   */
+  public function overrideNotice(BlockInterface $block) {
+    return [
+      'message' => [
+        '#type' => 'markup',
+        '#markup' => '<p>' . $this->t('This block cannot be edited in the Settings Tray form because it has configuration overrides in effect.') . '</p>',
+      ],
+      'link' => [
+        '#type' => 'link',
+        '#title' => $this->t('Edit block'),
+        '#url' => Url::fromRoute('entity.block.edit_form')
+          ->setRouteParameter('block', $block->id())
+          ->setOption('query', ['destination' => \Drupal::request()->get('destination')]),
+      ],
+    ];
+
+  }
+
+}
diff --git a/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.info.yml b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.info.yml
new file mode 100644
index 0000000000..89f9732feb
--- /dev/null
+++ b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.info.yml
@@ -0,0 +1,7 @@
+name: 'Configuration override test for Settings Tray'
+type: module
+package: Testing
+version: VERSION
+core: 8.x
+dependencies:
+  - settings_tray
diff --git a/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.services.yml b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.services.yml
new file mode 100644
index 0000000000..b23035bde2
--- /dev/null
+++ b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.services.yml
@@ -0,0 +1,5 @@
+services:
+  settings_tray_override_test.overrider:
+    class: Drupal\settings_tray_override_test\ConfigOverrider
+    tags:
+      - { name: config.factory.override}
diff --git a/core/modules/settings_tray/tests/modules/settings_tray_override_test/src/ConfigOverrider.php b/core/modules/settings_tray/tests/modules/settings_tray_override_test/src/ConfigOverrider.php
new file mode 100644
index 0000000000..0184a9e533
--- /dev/null
+++ b/core/modules/settings_tray/tests/modules/settings_tray_override_test/src/ConfigOverrider.php
@@ -0,0 +1,48 @@
+<?php
+
+namespace Drupal\settings_tray_override_test;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Config\ConfigFactoryOverrideInterface;
+use Drupal\Core\Config\StorageInterface;
+
+/**
+ * Provides an overridden block for Settings Tray testing.
+ *
+ * @see \Drupal\Tests\settings_tray\FunctionalJavascript\SettingsTrayBlockFormTest::testOverriddenDisabled()
+ */
+class ConfigOverrider implements ConfigFactoryOverrideInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function loadOverrides($names) {
+    $overrides = [];
+    if (in_array('block.block.overridden_block', $names)) {
+      $overrides = $overrides + ['block.block.overridden_block' => ['settings' => ['label' => 'Now this will be the label.']]];
+    }
+    return $overrides;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheSuffix() {
+    return 'ConfigOverrider';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function createConfigObject($name, $collection = StorageInterface::DEFAULT_COLLECTION) {
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheableMetadata($name) {
+    return new CacheableMetadata();
+  }
+
+}
diff --git a/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php b/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
index fcfecde400..98e8c59497 100644
--- a/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
+++ b/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\settings_tray\FunctionalJavascript;
 
+use Drupal\block\BlockInterface;
 use Drupal\block\Entity\Block;
 use Drupal\block_content\Entity\BlockContent;
 use Drupal\block_content\Entity\BlockContentType;
@@ -43,6 +44,7 @@ class SettingsTrayBlockFormTest extends OffCanvasTestBase {
     // cause test failures.
     'settings_tray_test_css',
     'settings_tray_test',
+    'settings_tray_override_test',
   ];
 
   /**
@@ -75,7 +77,7 @@ public function testBlocks($theme, $block_plugin, $new_page_text, $element_selec
     $page = $this->getSession()->getPage();
     $this->enableTheme($theme);
     $block = $this->placeBlock($block_plugin);
-    $block_selector = str_replace('_', '-', $this->getBlockSelector($block));
+    $block_selector = $this->getBlockCssSelector($block);
     $block_id = $block->id();
     $this->drupalGet('user');
 
@@ -267,8 +269,10 @@ protected function assertOffCanvasBlockFormIsValid() {
    * @param string $contextual_link_container
    *   The element that contains the contextual links. If none provide the
    *   $block_selector will be used.
+   * @param bool $has_confirm_form
+   *   Determines if the block form should be confirmed.
    */
-  protected function openBlockForm($block_selector, $contextual_link_container = '') {
+  protected function openBlockForm($block_selector, $contextual_link_container = '', $has_confirm_form = TRUE) {
     if (!$contextual_link_container) {
       $contextual_link_container = $block_selector;
     }
@@ -283,7 +287,9 @@ protected function openBlockForm($block_selector, $contextual_link_container = '
     $this->assertSession()->assertWaitOnAjaxRequest();
     $this->click($block_selector);
     $this->waitForOffCanvasToOpen();
-    $this->assertOffCanvasBlockFormIsValid();
+    if ($has_confirm_form) {
+      $this->assertOffCanvasBlockFormIsValid();
+    }
   }
 
   /**
@@ -321,7 +327,7 @@ public function testQuickEditLinks() {
       $this->enableTheme($theme);
 
       $block = $this->placeBlock($block_plugin);
-      $block_selector = str_replace('_', '-', $this->getBlockSelector($block));
+      $block_selector = $this->getBlockCssSelector($block);
       // Load the same page twice.
       foreach ([1, 2] as $page_load_times) {
         $this->drupalGet('node/' . $node->id());
@@ -577,4 +583,49 @@ protected function getTestThemes() {
     });
   }
 
+  /**
+   * Tests that blocks with configuration overrides are disabled.
+   */
+  public function testOverriddenDisabled() {
+    $web_assert = $this->assertSession();
+    $overridden_text = 'This block cannot be edited in the Settings Tray form because it has configuration overrides in effect.';
+    // Test a overridden block does not show the form in the off-canvas dialog.
+    // @see \Drupal\settings_tray_override_test\ConfigOverrider
+    $overridden_block = $this->placeBlock('system_powered_by_block', [
+      'id' => 'overridden_block',
+      'label_display' => 1,
+      'label' => 'This will be overridden.',
+    ]);
+    $this->drupalGet('user');
+    // Confirm the label is actually overridden.
+    $web_assert->elementContains('css', $this->getBlockCssSelector($overridden_block), 'Now this will be the label.');
+    $this->enableEditMode();
+    $this->openBlockForm($this->getBlockCssSelector($overridden_block), '', FALSE);
+    $web_assert->elementContains('css', self::OFF_CANVAS_CSS_SELECTOR, $overridden_text);
+
+    // Test a non-overridden block does show the form in the off-canvas dialog.
+    $block = $this->placeBlock('system_powered_by_block', [
+      'label_display' => 1,
+      'label' => 'Labely label',
+    ]);
+    $this->drupalGet('user');
+    // Confirm the label is not overridden.
+    $web_assert->elementContains('css', $this->getBlockCssSelector($block), 'Labely label');
+    $this->openBlockForm($this->getBlockCssSelector($block));
+    $web_assert->elementNotContains('css', self::OFF_CANVAS_CSS_SELECTOR, $overridden_text);
+  }
+
+  /**
+   * Gets the CSS selector for a block.
+   *
+   * @param \Drupal\block\BlockInterface $block
+   *   The block.
+   *
+   * @return string
+   *   The CSS selector for the block.
+   */
+  protected function getBlockCssSelector(BlockInterface $block) {
+    return str_replace('_', '-', $this->getBlockSelector($block));
+  }
+
 }
diff --git a/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php b/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php
index d3f446cf6a..86cca2c680 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php
@@ -9,6 +9,11 @@
  */
 abstract class OffCanvasTestBase extends JavascriptTestBase {
 
+  /**
+   * CSS selector for the off-canvas dialog.
+   */
+  const OFF_CANVAS_CSS_SELECTOR = '.ui-dialog[aria-describedby="drupal-off-canvas"]';
+
   /**
    * {@inheritdoc}
    */
@@ -83,7 +88,7 @@ protected function waitForOffCanvasToClose() {
    * @return \Behat\Mink\Element\NodeElement|null
    */
   protected function getOffCanvasDialog() {
-    $off_canvas_dialog = $this->getSession()->getPage()->find('css', '.ui-dialog[aria-describedby="drupal-off-canvas"]');
+    $off_canvas_dialog = $this->getSession()->getPage()->find('css', self::OFF_CANVAS_CSS_SELECTOR);
     $this->assertEquals(FALSE, empty($off_canvas_dialog), 'The off-canvas dialog was found.');
     return $off_canvas_dialog;
   }
diff --git a/core/tests/Drupal/Tests/Core/Config/ConfigTest.php b/core/tests/Drupal/Tests/Core/Config/ConfigTest.php
index 41c3e93c99..d5b71edc07 100644
--- a/core/tests/Drupal/Tests/Core/Config/ConfigTest.php
+++ b/core/tests/Drupal/Tests/Core/Config/ConfigTest.php
@@ -173,6 +173,7 @@ public function testSaveExisting($data) {
    * @covers ::setModuleOverride
    * @covers ::setSettingsOverride
    * @covers ::getOriginal
+   * @covers ::hasOverrides
    * @dataProvider overrideDataProvider
    */
   public function testOverrideData($data, $module_data, $setting_data) {
@@ -184,26 +185,40 @@ public function testOverrideData($data, $module_data, $setting_data) {
 
     // Save so that the original data is stored.
     $this->config->save();
+    $this->assertFalse($this->config->hasOverrides());
+    $this->assertOverriddenKeys($data);
 
     // Set module override data and check value before and after save.
     $this->config->setModuleOverride($module_data);
     $this->assertConfigDataEquals($module_data);
+    $this->assertOverriddenKeys($data, $module_data);
+
     $this->config->save();
     $this->assertConfigDataEquals($module_data);
+    $this->assertOverriddenKeys($data, $module_data);
+
+    // Reset the module overrides.
+    $this->config->setModuleOverride([]);
+    $this->assertOverriddenKeys($data);
 
     // Set setting override data and check value before and after save.
     $this->config->setSettingsOverride($setting_data);
     $this->assertConfigDataEquals($setting_data);
+    $this->assertOverriddenKeys($data, $setting_data);
     $this->config->save();
     $this->assertConfigDataEquals($setting_data);
+    $this->assertOverriddenKeys($data, $setting_data);
 
     // Set module overrides again to ensure override order is correct.
     $this->config->setModuleOverride($module_data);
+    $merged_overrides = array_merge($module_data, $setting_data);
 
     // Setting data should be overriding module data.
     $this->assertConfigDataEquals($setting_data);
+    $this->assertOverriddenKeys($data, $merged_overrides);
     $this->config->save();
     $this->assertConfigDataEquals($setting_data);
+    $this->assertOverriddenKeys($data, $merged_overrides);
 
     // Check original data has not changed.
     $this->assertOriginalConfigDataEquals($data, FALSE);
@@ -216,6 +231,15 @@ public function testOverrideData($data, $module_data, $setting_data) {
       $config_value = $this->config->getOriginal($key);
       $this->assertEquals($value, $config_value);
     }
+
+    // Check that the overrides can be completely reset.
+    $this->config->setModuleOverride([]);
+    $this->config->setSettingsOverride([]);
+    $this->assertConfigDataEquals($data);
+    $this->assertOverriddenKeys($data);
+    $this->config->save();
+    $this->assertConfigDataEquals($data);
+    $this->assertOverriddenKeys($data);
   }
 
   /**
@@ -449,6 +473,85 @@ public function overrideDataProvider() {
           'a' => 'settingValue',
         ],
       ],
+      [
+        // Original data.
+        [
+          'a' => 'originalValue',
+          'b' => 'originalValue',
+          'c' => 'originalValue',
+        ],
+        // Module overrides.
+        [
+          'a' => 'moduleValue',
+          'b' => 'moduleValue',
+        ],
+        // Setting overrides.
+        [
+          'a' => 'settingValue',
+        ],
+      ],
+      [
+        // Original data.
+        [
+          'a' => 'allTheSameValue',
+        ],
+        // Module overrides.
+        [
+          'a' => 'allTheSameValue',
+        ],
+        // Setting overrides.
+        [
+          'a' => 'allTheSameValue',
+        ],
+      ],
+      [
+        // Original data.
+        [
+          'a' => [
+            'b' => 'originalValue'
+          ],
+        ],
+        // Module overrides.
+        [
+          'a' => [
+            'b' => 'moduleValue'
+          ],
+        ],
+        // Setting overrides.
+        [
+          'a' => [
+            'b' => 'settingValue'
+          ],
+        ],
+      ],
+      [
+        // Original data.
+        [
+          'a' => [
+            'b' => 'originalValue'
+          ],
+        ],
+        // Module overrides.
+        [
+          'a' => [
+            'b' => 'moduleValue'
+          ],
+        ],
+        // Setting overrides.
+        [],
+      ],
+      [
+        // Original data.
+        [
+          'a' => [
+            'b' => 'originalValue'
+          ],
+        ],
+        // Module overrides.
+        [],
+        // Setting overrides.
+        [],
+      ],
     ];
   }
 
@@ -545,4 +648,38 @@ public function testSafeStringHandling() {
     $this->assertSame($safe_string, $this->config->get('bar'));
   }
 
+  /**
+   * Assert that the correct keys are overridden.
+   *
+   * @param array $data
+   *   The original data.
+   * @param array $overridden_data
+   *   The overridden data.
+   */
+  protected function assertOverriddenKeys(array $data, array $overridden_data = []) {
+    if (empty($overridden_data)) {
+      $this->assertFalse($this->config->hasOverrides());
+    }
+    else {
+      $this->assertTrue($this->config->hasOverrides());
+      foreach ($overridden_data as $key => $value) {
+        // If there are nested overrides test a combined key.
+        if (is_array($value)) {
+          $key = $key . '.' . key($value);
+        }
+        $this->assertTrue($this->config->hasOverrides($key));
+      }
+    }
+
+    $non_overridden_keys = array_diff(array_keys($data), array_keys($overridden_data));
+    foreach ($non_overridden_keys as $non_overridden_key) {
+      $this->assertFalse($this->config->hasOverrides($non_overridden_key));
+      // If there are nested overrides test a combined key also.
+      if (is_array($overridden_data)) {
+        $nested_non_overridden_key = $non_overridden_key . '.' . key($overridden_data);
+        $this->assertFalse($this->config->hasOverrides($nested_non_overridden_key));
+      }
+    }
+  }
+
 }