The old county jail was not attached to the courthouse. It was a free-standing building on the east side of the courthouse lawn. Shown below is the 1885 Sandborn Insurance map showing the location of the jail. While it was located close to the courthouse, it was not attached. It did have a fence which encircled the building and its yard which may have attached to the courthouse in some way.  

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The old jail was closed in October 1888 and the prisoners moved to the Travis County jail because of frequent jail breaks. The jail on Main Street was approved for construction during the county commissioners' court session on January 3, 1888. It's funding - contrary to what appears on the state historical marker - was through the sale of bonds. The land for the jail site was David Love's wagon yard which was purchased through the donation of funds by prominent Williamson County residents. The new jail was accepted by the county commissioners in January 1889 and prisoners began to be housed there.