The Old Jail is a limestone building. Much of the floor on the lower level is made of "Bandera Marble." This is a flagstone type rock found near Redfield in Bourbon County. At one time the entire structure was converted with rough stucco. The stucco was later removed except in the window recesses. This was patchy and cracked, so all the remaining stucco was removed in the spring of 1986 when many window and plaster repairs were made.

A few dangerous criminals and hundreds of minor offenders were confined in the jail over the years. Quite a few prisoners escaped confinement from the jail over the years, many by removing the iron bars on the windows or by cutting a hole in the roof. Only a few months after the jail was opened, a small mob of men overpowered the sheriff and removed on E.G. Dalson from the jail on the evening of June 27, 1870. He was then taken to a barn outside of Iola, KS and hung. He had been jailed on charges of murdering his stepson. Despite this incident, two adjoining counties began sending their criminals to Allen County for incarceration in the jail during the later 1870s.

In 1904, the county remodeled the jail and made cells in the upstairs area. The outside stairway was removed and the door sealed. The narrow stairway inside was built and the upstairs was divided into cells with steel doors and metal walls. There was a Women's Detention Cell and the room at the northwest was used as an office for the jailer or sheriff who also had a room or office in the Allen County Courthouse.With the opening of the new Allen County Courthouse and its modern jail facilities, the old county jai was finally closed in 1958. During the first several years, the Old Jail Museum was used to house all of the collections of the Historical Society that could not be placed in the Museum Room of the Courthouse. In 1977, the Old Jail was placed on the National Register of Historic Places by the U.S. Department of Interior.