Camp Dennison is an unincorporated community just outside Indian Hill in Hamilton County, Ohio, United States. Although it is unincorporated, it has a post office, with the ZIP code of 45111. During the American Civil War, Camp Dennison served as a military recruiting and training post for the United States Army Camp Dennison. It is named for William Dennison, the 24th Governor of Ohio and U.S. Postmaster General under President Abraham Lincoln.

Camp Dennison was a military recruiting and training post for the United States Army during the American Civil War. It was located near Cincinnati, Ohio, not far from the Ohio River. The camp was named for Cincinnati native William Dennison, Ohio's governor at the start of the war.

With the outbreak of the Civil War in 1861, George B. McClellan, commander of Ohio's state militia, was charged by Governor Dennison with selecting a site for a recruitment and training center for southern Ohio, a possible target for the Confederate States Army due to its Ohio River location and proximity to slave states such as Kentucky and Virginia, from which invasions could be launched. He chose a level tract of land near Indian Hill, Ohio, 17 miles from Cincinnati. It was close to the Little Miami Railroad, which could haul trainloads of volunteer soldiers to the new camp from throughout western and southern Ohio. The location had fresh water in the nearby Little Miami River and a paved turnpike that enabled troops to be quickly moved to Cincinnati in case of an emergency.

More than 50,000 Union soldiers were mustered in or out of service at Camp Dennison. As many as 12,000 occupied the camp at any one time. During Morgan's Raid in 1863, troops from Camp Dennison responded to the invasion by Confederate cavalry under Brig. Gen. John Hunt Morgan, as they had in 1862 when Cincinnati was briefly threatened by the cavalry of Albert G. Jenkins.

As the war progressed, shortly after the Battle of Shiloh a military hospital was established on the grounds of Camp Dennison, with over 200 beds situated in a series of wooden barracks. The nearby Waldschmidt Cemetery served as the temporary gravesite for 340 Union soldiers and 31 Confederate soldiers who were prisoners of war. The bodies were reinterred at Spring Grove Cemetery or at Camp Chase in Columbus in the late 1860s.

The end of the Civil War in 1865 eliminated the need for Camp Dennison, which was deactivated in September. A small community, Camp Dennison, Ohio, sprang up around the camp and hospital. Many of the later barns and homes used lumber and materials from the abandoned army camp.