 The regiment recruited its members starting on July 15, 1862, from the 4th Congressional District which included the Michigan counties of Barry, Ionia, Montcalm, Kent, Ottawa, Muskegon, Oceana, Newaygo, Mecosta, Mason, Manistee, Grand Traverse, Leelanau, Manitou, Osceola, Emmet, Mackinac, Delta, and Cheboygan.The 21st Michigan Infantry rendezvous was at Ionia.Among the ranks were future prominent Michigan politicians John Avery and Charles E. Belknap.