Montgomery City is a city in and the county seat of Montgomery County, Missouri, United States. The population was 2,811 at the 2020 censu…Montgomery City is a city in and the county seat of Montgomery County, Missouri, United States. The population was 2,811 at the 2020 census. Montgomery was platted in 1853, taking its name from Montgomery County. A post office called Montgomery City has been in operation since 1857.