[3] It is named for Hugh Mercer, an officer in the American Revolutionary War.

Land south of the Greenville Treaty Line was still part of Darke County.

An act establishing and fully organizing Mercer County took place on January 2, 1824.

In the mid to late 1800s, Mercer County became home to many German immigrant farming families.

The highest point is on the southern county line at 1071 feet above sea level.

This point is located on the northern county line where the St. Marys River crosses over.

The first section begins in southern farmland in the county and flows through the town of Montezuma, Ohio and into Grand Lake St. Marys.

The other section of the creek begins as a spillway and empties into the Wabash River.

Beaver Creek was originally one piece, but was split into two sections after the construction of Grand Lake.

Mercer County's elected commissioners are: Jerry Laffin, Rick Muhlenkamp, and David Buschur.

As of the 2010 United States Census, there were 40,814 people, 15,532 households, and 11,172 families living in the county.

[16] Prior to 1940, Mercer County was primarily Democratic, only voting Republican once from 1856 to 1936 for Ohioan Warren G. Harding in 1920.

The county is the fictional setting of the Amazon Prime Video series Tales from the Loop.