is a city in Miami County, Ohio, United States. The population was 21,999 at the 2000 census. It is the county seat of Miami County and is part of the Dayton Metropolitan Statistical Area.
Troy was one of the cities impacted by severe flooding in the Great Dayton Flood of 1913.
According to the United States Census Bureau, the city has a total area of 9.8 square miles (25.3 km²), of which, 9.7 square miles (25.1 km²) of it is land and 0.1 square miles (0.2 km²) of it (0.72%) is water.