Deerfield Township, one of the eleven townships of Warren County, Ohio, United States, is located in the southwest corner of the county. The most urbanized of the eleven, it had 25,515 people in the 2000 census, down from the 26,359 in 1990. (The drop is because the city of Mason, which was included in the 1990 figures, withdrew from the township in February 1997.) Until 1997, Kings Island amusement park was in the township. Statewide, other Deerfield Townships are located in Morgan, Portage, and Ross Counties.