How to Determine a County by Zip Code
There are more than 42,000 zip codes in the United States, and according to January 2011 estimates, there are an average of nearly 7,300 residents in each. The zip codes are unique to an area of the country. Simple Internet searches can provide data about each of the zip codes, including the city, county and state.
Visit the U.S. Census Bureau's state and county information page using the link in Resources.
Enter the zip code into the box requesting a zip code, town name or city. In the nearby check box, select "All states" instead of a specific state as your search criteria.
Press the button marked "Go." The website will return the name of the city, county and state represented by the zip code you entered.