Here is a handy link for you.
In researching genealogy, let's say you come across a name of a new town where your ancestors lived in America and now you would like to research that town further. In order to do that, first you must determine what county the city is located in as many of the research sources are enabled by county. Here's a great site that will quickly find that county for you by searching for the city and state. Handy, huh?
Zip-Codes.com
Now that you have the name of the county, you can head to Google maps to search for the county and see it on the map. Keep in mind that county boundaries move as they were being divided to create new counties. This would effect what county you go to in order to do research.