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.
Normal module installation applies, however, there are some preparatory steps.
Note: Ip2cc installs a VERY large database table (30+ MB); it will take a little while. Wait for it.
Note: As a convenience, the messages include a link to take you straight to the settings page.
Yout site should now reject registration attempts from any countries not in your list.
I've included a sample error page for registration denial. It should require minimal customization.
Please post support or feature requests, or bug reports on the project page, not in the general forums.