Trotwood is a city in Montgomery County, Ohio, United States. The population was 23,070 at the 2020 census. A suburb of Dayton, it is part of the Dayton metropolitan area. The city is served by the Trotwood-Madison City School District.

Montgomery County is in the southwestern part of the U.S. state of Ohio. At the 2020 census, the population was 537,309, making it the fifth-most populous county in Ohio. The county seat is Dayton. 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. Montgomery County is part of the Dayton, Ohio, Metropolitan Statistical Area.