Camp Dennison is a census-designated place (CDP) just outside Indian Hill in southern Symmes Township, Hamilton County, Ohio, United States. Although it is unincorporated, it has a post office, with the ZIP code of 45111. The population was 375 at the 2010 census. During the American Civil War, Camp Dennison served as a military recruiting and training post for the United States Army (see Camp Dennison). It is named for William Dennison, the 24th Governor of Ohio and U.S.