Hamilton is a city in and the county seat of Butler County, Ohio, United States. Located 20 miles north of Cincinnati along the Great Miami Ri…Hamilton is a city in and the county seat of Butler County, Ohio, United States. Located 20 miles north of Cincinnati along the Great Miami River, Hamilton is the second-largest city in the Greater Cincinnati area and the tenth-largest city in Ohio. The population was 63,399 at the 2020 census. Most of the city is served by the Hamilton City School District.