The Genealogy of Your Counties
We're used to thinking of people having a genealogy. People have parents and some people have children. The same is true of counties in the United States. A county usually has another county it was formed from and some counties have had other counties split off from it. This can have a huge impact on your research.
Counties were formed as populations grew and moved. For example, when Indiana became a state on 11 December 1816, there were 15 counties. Today, there are 92. The creation of the counties followed the growth and migration of the population. In Indiana, this means that the older counties are in the southern part of the state, where Indiana was first settled; the newer counties are in the north, where the population spread.
Early counties were much larger than they are today. Trumbull County, Ohio, for example, took up most of the northeast quarter of Ohio in 1803. As more people moved into the area and settled in specific areas, counties such as Ashtabula, Geauga, and Mahoning were split off from it. Today, Trumbull County is comparable in size to Ohio's other counties.
Why It Matters
When a county spawned a new county, the records that had been created before the "birth" of the new county stayed where they were. Blackford County, Indiana was formed in 1838 from Jay County. Let's say that in 1837 a minister performed a marriage in a spot that later became Blackford County. The resulting marriage record would be found in Jay County, because that's where it was when the event happened.
It helps to know the origins of counties when looking at the census. If you have a family in Newton County, Indiana in the 1860 census, you won't find the family there in the 1850 census. Newton County was formed from Jasper County in 1859. Jasper County would be a good place to start looking for the family in 1850.
Finding the Parent County
Red Book: American State, County, and Town Sources is an excellent guide for finding parent counties. You can search for the county you're looking for and get a summary of the county's origins. Houghton County, Michigan's page shows that it was formed in 1845 from Marquette, Ontonagon, and Schoolcraft counties.
If you like visual representations, check out Nancy Hendrickson's Expert Series article "Finding Historical U.S. County Boundaries Using Google Earth." It's a fun way to see how counties have changed.
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