Try the Newberry Library’s Atlas of Historical County Boundaries for US genealogy research at the county level.
The Atlas of Historical County Boundaries is a powerful historical research and reference tool in electronic form. The Atlas illustrates the size, shape, and location 
of every county in the US and the District of Columbia over time.
Searching the Atlas of County Historical Boundaries
If you’re uncertain about the county you’re looking for, start your search at the state level.
This online resource also includes non-county areas, and unsuccessful authorizations for new counties. Changes in county names and organization are included. The principal sources for these data are the most authoritative available: Sources for the Atlas include sessions for laws of the colonies, territories, and states that created and changed the counties.
The Atlas of Historical County Boundaries assists genealogists seeking records of past events. Researchers of census and state and local history projects will find this site useful too.
About the Atlas
The Atlas is designed to be as comprehensive as possible. Every day is covered, from the early 1600s to 2000. Geographically, the range for each state includes all the territory within its bounds in 2000, regardless of what government created or altered a county there. Other territories are included for the state’s jurisdiction at an earlier time.
If you are fortunate enough to be able to research in person at The Newberry Library in Chicago, do please go. Fortunately, the Atlas they’ve created is a wonderful tool for researchers everywhere.
For more Sassy Jane posts on maps that help your family history research, click here.
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