Union is a city in Montgomery and Miami Counties in the U.S. state of Ohio. The population was 6,419 at the 2010 census. It is part of the Dayton Metropolitan Statistical Area.
The coordinates for The City of Union are 39°54′1″N 84°18′49″W (39.900154, -84.313494).
According to the United States Census Bureau, the city has a total area of 8.602 square miles (22.28 km2), of which 8.522 square miles (22.07 km2) is land and 0.08 square miles (0.21 km2) is water. The Stillwater River runs on its east side.
Ironically, Union lies west of West Union, Ohio, the county seat of Adams County approximately 60 miles east of Cincinnati. Union and West Union are not adjacent to each other, actually being approximately 120 miles from each other.
One major state highway, State Route 48, runs North and South through Union. In Union, State Route 48 is known as Main Street. Union is 4 miles North of Interstate 70
Other notable streets in Union include Martindale Road, Sweet Potato Ridge Road, and Phillipsburg-Union Road.