Trenton is a city in northeastern Butler County, Ohio, United States, west of Middletown. Originally in Madison Township, it later annexed land in Wayne Township. The population was 8,746 at the 2000 census.
Trenton is located at 39°28′55″N 84°27′34″W / 39.48194°N 84.45944°W / 39.48194; -84.45944 (39.481909, -84.459460).
According to the United States Census Bureau, the city has a total area of 3.8 square miles (9.8 km²), all of it land.