Pinpointing the county in which your family lived during a given year is easy, thanks to the Newberry Library's Atlas of Historical County Boundaries.
Changing boundaries have long challenged genealogy researchers: Your ancestors could have records in multiple counties or states, even if they didn't move an inch. For example, in 1776, Fincastle County, Va., was trisected into Kentucky, Washington and Montgomery counties. In 1780, Kentucky County became Fayette, Jefferson and Lincoln counties; then in 1792, those became the state of Kentucky. It's hard to keep up -- but if you don't, it's almost impossible to track down records.
Today, pinpointing the county where your family lived during a given year is easy, thanks to the Newberry Library's Atlas of Historical County Boundaries. Not only can you view interactive maps showing changing boundaries for each state, but you also can download a boundary timeline for every US county. You can even import the data into free Google Earth software and use the time slider to view county line changes over time. These are our favorite ways to use the atlas: