[3] The county was created on March 1, 1818, and was named for General George Rogers Clark,[4] a hero of the American Revolution.

As of the census[11] of 2020, there were 136,001 people, 54,862 households,[12] and 35,354 families living in the county.

29.1% of all households were made up of individuals, and 4.0% had someone living alone who was 65 years of age or older.

[20] As of the 2010 United States census, there were 138,333 people, 55,244 households, and 36,906 families living in the county.

[24] As of the census[25] of 2000, there were 144,742 people, 56,648 households, and 39,370 families living in the county.

23.8% were of German, 21.6% American, 10.4% Irish and 8.7% English ancestry according to Census 2000.

26.00% of all households were made up of individuals, and 11.10% had someone living alone who was 65 years of age or older.

[28] That same year, Dayton and Springfield were grouped together as the Dayton-Springfield Metropolitan Statistical Area.

The new MSA consisted of four counties – Clark, Greene, Miami, and Montgomery.

[29] This arrangement remained unchanged until 2003, when the MSA was split with Springfield's newly defined metropolitan area including only Clark County.

[30] Clark County has voted Republican in every presidential election since 2004, with Donald Trump receiving 57% of the vote in 2016, a deviation from the usual tight results in the county.

In 2012, Mitt Romney won the county, but by only 523 votes out of 64,301 cast for president.

[31] County Commissioners - (President) Melanie Flax Wilt (R), Rick Lohnes (R), and Lowell McGlothlin (R) Sheriff - Deb Burchett (R) Recorder - Nancy Pence (R) Treasurer - Pamela Littlejohn (R) Auditor - Hillary Hamilton (R) Prosecuting Attorney - Dan Driscoll (R) Coroner - Susan L. Brown, DO (D) Judicial Municipal Court Clerk of Courts - Sheila Rice (D) Judges - Valerie Wilt (R), Stephen A. Schumaker (R), Daniel Carey (R) Common Pleas Court Clerk of Courts - Melissa Tuttle (R) General Division - Judges Douglas Rastatter (R) and Brian Driscoll (R) Domestic Relations - Judge Thomas Capper (R) Juvenile Court - Judge Katrine M Lancaster (R) Probate - Judge Richard Carey (R) Public school districts include:[33]