Simple Geo targeting

I would like some very simple and limited Geo targeting functionality.

I want to display a different footer depending on whether the visitor is from US or not. Ideally the code should be something like this:

<?php if ( visitor is from usa ): ?>
<?php get_footer('us'); ?>
<?php else: ?>
<?php get_footer('other-countries'); ?>
<?php endif; ?>

I would prefer the solution to be as simple and light as possible.

via Chebli Mohamed