Exact spelling required. You'll be able to view a list of counties you've named so far after you've named at least 3 of them. Clicking on the name of the county will highlight it on the map. If you wish to admit defeat, clicking the I Give Up button at the bottom of the map will list all 58 counties.
Designed and programmed by Sean Matthew "Mangels" Hall. The map is courtesy of Wikipedia user awmcphee. If you liked this, check out Chris Arvin's game that challenges you to name every street in San Francisco, if you haven't already. It partially inspired me to make this game. Please direct feedback to m@mattmangels.com.