I would like to recommend below channels for your purpose:
1. Targeting country specific keywords for your sites and using them in page contents and back links
2. Using Google Places for promotion purpose.
There is an option in there to target to just a specific country. However, this almost always result in you receiving less overall traffic from the search engines. All of the international traffic you would receive will be filtered out, but you won't necessarily receive significantly more traffic within the US.
The advantage to doing this is if you sell a product just within the US, and are getting a lot of international traffic, you can't monetize the int'l traffic but it is still costing you a lot of money to have a powerful enough web server to handle it all. You'd rather your server only had to deal with traffic you can monetize.
> 2. Get the domain name for that particular country.
The problem is that, while this is true for most countries, the US does not really have a country-specific domain. The .com domain is considered country-neutral in Google's eyes.