How to Use the Atlas of Historical County Boundaries

Steps to finding old county boundaries to further your research

County boundaries have often changed over time, so you may be looking for your ancestor in the wrong county. The Atlas of Historical County Boundaries is a resource that can confirm which boundary to research since it gives you old U.S. county boundaries for all 50 states. It can be a very useful tool for knowing which county to look for when searching for your ancestors.

Step 1

Visit the Atlas of Historical County Boundaries website


Step 2

Select the state you wish to search for by clicking the map, using the drop down menu on the top right, or clicking the list of states link.


Step 3

Once you select a state, you will be presented with several options. Choose the top option: "View Interactive Map."


Step 4

You will now be presented with the interactive map. Here you can zoom, move around the map (by holding down and moving the mouse) and look for your chosen location.


Step 5

On the left you will see the dates of all the historical border changes. Choose a date nearest to the time your ancestor lived. By clicking on the date, you will see the borders shift on your map. You can then evaluate what county your ancestor lived in.


All known border change dates are listed in the dropdown box. If you want to see a date in between border change dates, choose the closest date before your event. For example, if you want to see Dakota Territory boundaries in 1880, choose the date "1879-10-01" which were in effect until the next change on "1881-02-08."

For more information on using the map you can also visit this page on the Atlas of Historical County Boundaries website.

Need help finding more records? Try our genealogical records directory which has more than 1.3 million sources to help you more easily locate the available records.

Related Topics on This Site