thumb|right|Lawrenceburg on the Ohio River, from the air. AEP's [[Tanner's Creek Generating Station at lower-left.]]
Dearborn County is one of 92 counties of the U.S. state of Indiana. Located on the Ohio border near the southeast corner of the state, Dearborn County was formed in 1803 from a portion of Hamilton County, Ohio. In 2020, the population was 50,679. The county seat and largest city is Lawrenceburg.
Dearborn County is part of the Cincinnati, OH-KY-IN Metropolitan Statistical Area.
History
In 1803, following Ohio's admission to the Union, a wedge, or pie shaped, remnant of the former Northwest Territory along Ohio's southwestern border was ceded to Indiana Territory and organized as Dearborn County. It was named after Henry Dearborn who was U.S. Secretary of War at that time. Lawrenceburg was then designated as the county seat.
All or part of seven other present day counties were carved from the original county with the present boundaries being established in 1845. The region, nicknamed the "Gore", slices through the present-day counties of Dearborn, Franklin, Ohio, Randolph, Switzerland, Union, Wayne and Fayette. Subdivision of Dearborn County began in 1811 with the formation of Franklin and Wayne Counties, followed by Switzerland in 1814. A contention existed between the towns of Lawrenceburg and the mostly German-speaking immigrants that dominated Rising Sun over the favored status of Lawrenceburg as the county seat. The rivalry between the two towns was resolved in 1844 when the Indiana State legislature separated the portion of Dearborn County south of Laughery Creek and created the last and smallest Indiana county, county of Ohio on March 1, 1844, with Rising Sun designated as its county seat.
Geography
According to the 2010 census, the county has a total area of , of which (or 99.22%) is land and (or 0.77%) is water.