In the 1890's and early 1900's, Thermopolis was a favorite resort of Wyoming's outlaws. It was the nearest town to many of their hideouts, and notorious characters such as Butch Cassidy, the Sundance Kid, and Kid Curry were popular figures around town. They had many friends in Thermopolis, for they were usually careful to commit their robberies farther away from home. Tom Skinner's saloon was one of the outlaws' favorite haunts, and he supposedly named it in their honor, after their Hole-in-the-Wall hideout about 70 miles from Thermopolis.

Many of the founders of the Pioneer Association and the Museum had known the outlaws in their younger days. Minnie Brown, one of the early Pioneer Association members, was the widow of Marion F. Mike Brown, who was known to have hidden Butch Cassidy from pursuing Sheriff's posses. Mrs. Brown's photo albums provided many of the historic photographs in the Museum collection. Among Minnie Brown's photographs is one of the Sundance Kid and his girlfriend Etta Place, which may have been given to Mike Brown by Sundance himself.