Are you creating a country portal or a site dedicated to a specific country?
The Register Country module is designed to intercept new registrations and check if the IP address being used is registered to a country that the site administrator has chosen. In this way, you may limit sign ups to your site to specific countries.
The IP2CC module is required.
You might also be interested in the GeoUser module.
For more information, read the documentation (link below).
New maintainer wanted
This was a simple module done for a specific request. I no longer even have a way to test it. I will not port it to D7. If you are interested in this module, please post an issue to take it over.