Montgomery County is in the southwestern part of the U.S. state of Ohio.

[3] The county was named in honor of Richard Montgomery, an American Revolutionary War general, who was killed in 1775 while attempting to capture Quebec City, Canada.

[4] Montgomery County is part of the Dayton, Ohio, Metropolitan Statistical Area.

[5] As of the census of 2000, there were 559,062 people, 229,229 households, and 146,935 families living in the county.

30.40% of all households were made up of individuals, and 10.10% had someone living alone who was 65 years of age or older.

As of the 2010 census, there were 535,153 people, 223,943 households, and 138,060 families living in the county.

The last Democrat to win the county by double digits was Lyndon B. Johnson in 1964, while the last Republican to do so was George H. W. Bush in 1988.