Camp Dennison served during the Civil War as a place where organizations were mustered into or out of U.S. service from 1861 to 1865. Units associated with the camp included first three months infantry service in April 1861 in the 4th, 5th, 6th, 7th, 8th, 9th, 10th, 11th, and 12th Infantry; three-year infantry service in the Dennison Guards, the 4th Independent Company Sharpshooters, the 8th Independent Company Sharpshooters, and the 2nd, 3rd, 4th, 5th, 6th, 8th, 9th, 10th, 11th, 12th, 13th, 17th, 28th, 34th, 39th, 47th, 50th, 52nd, 54th, 57th, 70th, 79th, 83rd, 89th, 106th, and 108th O.V.I.; three-year cavalry service in the 4th, 5th, 9th, and 11th and the 3rd and 6th Independent Company Ohio Artillery; three-year artillery service in the 2nd Regiment Heavy Artillery and the 1st Ohio Volunteer Light Artillery Independent Battery, as well as the 5th, 8th, 10th, 14th, 15th, 18th, 21st, and 24th Independent Battery Light Artillery; three-year brigade band service in the 3rd Brigade, 3rd Division, 4th Army Corps; one-year infantry service in the 175th, 181st, and 183rd; six-month cavalry service in the 4th Independent Battalion; and one hundred days infantry service in 1864 in the 138th, 139th, 146th, 147th, 149th, 153rd, 154th, 155th, 156th, 165th, and 168th.