Loomis was on the board of directors of the Chicago Relief and Aid Society, a charity for those left homeless and destitute after the fire of 1871. He donated money and time to the society and similar charities for twenty years. Loomis helped organize George H. Thomas Post Number 5 of the Grand Army of the Republic. In 1879, Loomis founded the Illinois Commandery of MOLLUS, the Military Order of the Loyal Legion of the United States, and became its commander in 1884, succeeding Philip Sheridan. Loomis also served as treasurer in 1879 and head of the U.S. Volunteers from 1880 to 1883