The qualifications for membership in the company were unquestioned loyalty to the Union cause, undaunted courage and the skillful use of the rifle or revolver. Their headquarters were at the "Six-mile House," so called because it was six miles from Wyandotte (Kansas City) on the Leavenworth Road. This house was erected in the winter of 1860-61 by Joseph A. Bartels, whose son, Theodore, one of the best pistol shots on the border, was a member of the Red Legs. The company was commanded by Captain George H. Hoyt, the lawyer who defended John Brown at Charleston, Virginia. Other members were Jack Harvey, a brother of Fred Harvey, of Santa Fe Wild Bill "; Joseph B. Swain, nicknamed "Jeff Davis," afterward captain of Company K. Fifteenth Kansas; "Red" Clark, of Emporia, whom General Ewing said was the best spy he ever had; John M. Dean, who was one of the organizers; and W. S. Tough, for many years proprietor of the horse market at the Kansas City stockyards. Still others, of less note, were Harry Lee, Newt Morrison, Jack Hays, James Flood, Jerry Malcolm, and Charles Blunt, often called "One-eyed Blunt."

William W. Denison, assistant adjutant-general of Kansas some years after the war, was a private soldier in the Eleventh Kansas, and was one of the detail to enforce General Thomas Ewing's General Order No. 11. On that occasion he wore the red leggings of the organization, which came to be recognized as "a badge of desperate service in the Union army." Generals Ewing and Blunt usually had several of the Red Legs on their payrolls, where they received often as much as $7 per day on account of the hazardous service they were required to render.

In course of time the term "Red Leg" became general along the border. William E. Connelley, in his Quantrill and the Border Wars, said: "Every thief who wanted to steal from the Missouri people counterfeited the uniform of the Red Legs and went forth to pillage. This gave the organization a bad name, and much of the plundering done along the border was attributed to them, when, in fact, they did little in that line themselves. There were some bad characters among them—very bad. But they were generally honest and patriotic men. They finally hunted down the men who falsely represented themselves to be Red Legs, and they killed every man found wearing the uniform without authority."

Albert R. Greene, a member of the Ninth Kansas Cavalry, was personally acquainted with many of the Red Legs and was also well acquainted with the nature of their service. Concerning them and their work he said: "There was not one of them but performed valuable service for the Union cause, and, so far as I know and believe, always within the rules of civilized warfare. That the organization was disbanded before the close of the war was owing more to the fact that the necessity for its existence had ceased than because a few of its members had thrown off the restraints of discipline. . . . It is enough to say for the propriety and wisdom of such an organization as the Red Legs, that it did more to protect the homes of Kansas than any regiment in the service, and was the organization of all others most dreaded by William Quantrill."