How to Map Old County Boundary Lines

How to Map Old County Boundary Lines

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:

1. On the Atlas of Historical County Boundaries home page, click a state on the map. A page opens with a menu of options — you can choose to launch an interactive map, get historical commentary, view an index of county chronologies and more. Below the image of the state is an explanation of each option.

2. Click the Interactive Map option. At the upper left is the date range the map covers, spanning the creation of the first county (or unsuccessful county proposal) through the year 2000. Note that historical lines are in black; modern boundaries are in brown and white. Here, you can see Florida’s 1825 boundaries.

3. Select the date you want from the pull-down menu in the upper-right corner and click Refresh Map. Changing the Florida date to 1900 produces a far different boundary map.

4. Zoom in, pan across the map, print and do other tasks using the tools on the left side of the page. Two options I like are Info and Measure (see arrows). Click the Info button, then click on a county to pop up a box of historical information. To use the Measure button, select it, then click anywhere on the map to place a red dot there. Now, wherever you move your mouse, you’ll get the distance on the map from the dot to your mouse pointer.

5. Below the map, click Chronologies, then Individual County Chronologies for detailed information about boundary changes for each county. Many counties have confusing and convoluted histories, and this is where you’ll find exact information.

6. Another way to view historical boundaries is to export data from the Atlas into Google Earth. Back on a state’s page, click Download KMZ Files. This will download a compressed file (with the ZIP extension) to your computer. Double-click the file to unzip it. The unzipped file will have a name like this: FL_Historical_Counties.kmz.

Next, open Google Earth. Click File > Open from the main menu bar, and navigate to the unzipped KMZ file. It’ll be added to the Temporary Places panel. Google Earth will automatically find the state and overlay its historical county boundaries on an aerial photo. Here, you can see Florida’s development in 1826. (New to Google Earth? The DVD Google Earth for Genealogy contains helpful video tutorials.)

7. When you import historical data into Google Earth, a time slider appears. Move the slider to view boundaries at a specific date or to launch an animation showing the changes. Adjust the animation speed by clicking the wrench icon on the slider.

Experiment with importing the KMZ files for two states your family lived in, then set the animation to slow. You’ll get a visual reference of what area was formed first and how the counties developed in relation to one another.


From the September 2011 issue of Family Tree Magazine

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