Union Troops
Custer's Irregulars are a mix of actual Union Soldiers loyal to Custer personally (including the remains of the 7th Cavalry) and a rough mix of freebooters and mercenaries drawn by Custer's talk of whipping the Sioux and taking the Ghost Rock of the Black Hills by force. They all wear the uniform of Union Troops, though, and have a semblance of discipline. Custer's current goal is to hold Deadwood through the winter, until the spring thaws make a military campaign against the Sioux a reality. While there, Custer intends to fortify the town and set up forts to "protect" the miners (which mostly amounts to shaking them down for tribute to keep the war effort going).