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.
Geography
The county has a total area of , of which is land and (0.6%) is water.
Adjacent counties
- Miami County (north)
- Clark County (northeast)
- Greene County (east)
- Warren County (south)
- Butler County (southwest)
- Preble County (west)
- Darke County (northwest)
Major highways
- 20px Interstate 70
- 20px<br>20px Interstate 70 Alternate
- 20px Interstate 75
- 25px Interstate 675
- 20px U.S. Route 25
- 20px U.S. Route 35
- 20px U.S. Route 40
- 20px State Route 4
- 20px State Route 48
- 20px State Route 49
- 25px State Route 123
- 25px State Route 201
- 25px State Route 202
- 25px State Route 235
- 25px State Route 444
- 25px State Route 725
- 25px State Route 741
- 25px State Route 835
National protected area
- Dayton Aviation Heritage National Historical Park (part)