Posted by Ancestry Team on November 19, 2013 in Research, Website

It probably doesn’t come as a surprise that maps today don’t reflect accurately the areas where our ancestors lived long ago. Roads have changed. New towns have appeared (and some have disappeared). What you might not realize is that the counties themselves might have changed. Those changes can have a huge impact on your research.

Most states didn’t become states with their current number of counties. Ohio, which has 88 counties today, had only nine counties when it became a state in 1803. So how do you add more counties? You take the counties you have and chop them into smaller pieces. With each new county that is created comes a new place for records to be created.

So what does this mean for our research? Let’s say you have a family who shows up in Noble County, Ohio in the 1860 census. You look for them in 1850, but you can’t find that family listed in Noble County. Turns out you’re not going to find them in there in 1850, because Noble County wasn’t formed until 1851.  It might have been the county line that moved, giving your ancestors a different county of residence without ever leaving home.

It’s not just the census that is impacted by changes in county boundaries. Records stay where they were created. That means vital records, land records, court records – any records created by the county government – are going to stay in that county. When a new county was formed, they didn’t go through the marriage records, for example, and say, “Ok, which of these weddings were performed in townships that moved over to the new county?” (Occasionally, you will find “new” counties that copied over land records from parent counties, but those are by far the exception.) The records stayed in the county where they were first created.

The Genealogy of a County

Learning when a county was formed and what county (or counties) was its “parent” will help you find the records. The Wiki contains Red Book: American State, County, and Town Resources. Scroll down to the Table of Contents and click on the state you’re interested in. On the new page, click on the link to that state’s county resources. Here is the page for Ohio: Wiki - Ohio

You’ll find a chart showing each county, when it was formed, the parent county/counties, and the dates that various records started in that county. Below is the top of the chart of the Ohio counties. Wiki - Ohio Counties

Let’s say you find your ancestors living in Auglaize County, Ohio in the 1850 census. The husband, wife and all of the children are listed as being born in Ohio. Based on the age of the children, it looks like the husband and wife were married in the early 1840s. Looking at the chart, we see that Auglaize County wasn’t formed until 1848. If you don’t find their marriage record there, the next places to look would be Allen and Mercer counties, because Auglaize was formed from them.

When you’re working on your genealogy and you’re not finding your people in the area where you think they should be, take a look at the genealogy of the county. You might find that the county changed.



  1. Amy Crow

    Robin — that is a cool site! Very good for seeing exactly how the boundaries changed. Another site that does that is the Newberry Library’s Atlas of Historical County Boundaries What I like about the tables in the Wiki is being able to look up a specific county and easily see the date it was created and what counties it was formed from. (And the map geek in me loves the graphical boundaries like from Newberry and the site you shared!)

  2. Charles Bottomlick

    Hey Ancestry,

    Do you think in the near future you may have a near stable site that is not constantly undergoing some sort of maintenance or unavailable as it is now ?

    I can’t imagine any other subscription service that’s run so amateurish as this one.

  3. Hi,
    A few years ago, I built a free Google Maps online tool based on the above Newberry site. Lots of people have found it very valuable.

    Just type in a present-day address, city, zipcode or the like and the date or historical year of interest and you’ll see a map of those boundaries as of that date, along with details on the boundary change, etc.


  4. Adriana

    Thank you so much, everyone. I have run into this problem numerous times over the years. I search the next or previous census in the same county for a family, get zero results, and am left wondering if they 1) moved, 2) died, 3) the county boundaries changed, 4) the county no longer exists, and 5) what the adjacent counties are during that period. Argh!

    I use Google and can sometimes get an answer, but often the information is surprisingly hard to find. I really appreciate the resources.

  5. Madolyn Hayne

    This is very important info for my research in Virginia, thanks for
    all the places to find how counties changed during the 1600’s to 1900’s
    when I suspect my ancestors didn’t move at all, but counties changed around them. Will make it much easier to determine where they lived.
    Thanks for all the info!

  6. skm

    In my state, rural townships (6 miles x 6 miles, usually), occasionally become incorporated cities. For example, the former Avon Township became the city of Auburn Hills in the year 1984. Some communities existed ONLY as post offices, even if the community showed up on maps. There has never EVER been an incorporated city or town of “Union Lake, Michigan”, yet it was our mailing address for decades and definitely appears on many maps–it was only/still is a post office for four separate townships. These are all mid- to late- 20th century changes, there are earlier ones.

    Good luck with those place names! I have already seen someone on line puzzling over why my own dad seemed to have lived in a PO Box, without taking the time to find out that it was just a rented Post Office, not a physical address.

  7. Ginger Horning

    Thanks for the info I have been trying to find people in Ohio over and over again with no luck I never gave it a thought that boundries might have changed. Will try a new search using this new info. Again Thank You

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