If you ever need a map showing the counties of just one state, complete with county name labels, you can find links to those on the aptly titled County Maps of all 50 U.S. States page.
For example, clicking the Iowa County Map link on that page will take you to the County Lines on Google Maps tool already filtered to show just Iowa counties, complete with labels. It looks like this:
Once on the page, you can zoom in, turn on city limits and townships in the lower left corner, and so on.
Also, if you need to find the county you are currently in (based on your mobile device’s location), try the What County Am I In? tool. And companion tools What City Am I In? and What Township Am I In? — they do what they say on the tin. ;)