Camp Dennison was located in the town of Germany, Ohio, seventeen miles north of Cincinnati. George McClellan, a general in the Ohio militia, chose Germany as a site for a training camp for volunteers during the American Civil War. The camp was named for William Dennison, Ohio's governor. Located along the Little Miami River, Camp Dennison was strategically located near Cincinnati, the Ohio and Little Miami Rivers, and the Little Miami Railroad. The rivers and railroad provided quick transportation from various parts of Ohio and surrounding states. The presence of troops at Camp Dennison would also provide Cincinnati with soldiers to protect this important manufacturing city from Confederate attack. Camp Dennison encompassed more than five hundred acres of land.

The task of laying out the camp fell to Colonel William Rosecrans. Construction of barracks began in 1861. The barracks provided homes for the more than fifty thousand men who passed through the camp during the Civil War. They were located to the south of the Little Miami Railroad. In 1862, military officials established a hospital on the northern edge of the camp, just to the north of the railroad. It eventually had room for 2,300 sick or injured soldiers.

The soldiers at Camp Dennison usually remained in the area for only a short time. After receiving some training, military officials would send the men into the South to war against Confederate forces. In 1863, men currently undergoing training at Camp Dennison helped defend the Little Miami Railroad and Cincinnati from General John Hunt Morgan and his raiders. Morgan's men succeeded in capturing and destroying a supply train but failed in destroying an important railroad bridge across the Little Miami River.

Upon the Civil War's conclusion, Camp Dennison was abandoned. Local residents dismantled the barracks and hospital, scavenging building supplies to construct their own homes from the former campsite. Hoping to increase the community's population, Germany residents changed the town's name to Grand Valley, but the railroad continued to use Camp Dennison to identify the local station.