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 11,869 at the 2010 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). The city lies on the west bank of the Great Miami River.