Flatonia Tower No. 3 is a two-story rail tower clad in wood siding with metal, hipped roof with wide eaves. On the first level of the primary façade, there is a single wood paneled door with historic hardware. On the first level's secondary elevations, there are single and paired, divided-light, double-hung, wood windows. The building has an exterior metal staircase that leads to an entrance on the second story. The upper level door has divided lights over wood panels and the second story is wrapped with paired or grouped divided-light, double-hung, wood windows.
The building was constructed by the Galveston, Harrisburg & San Antonio Railroad in 1902 to serve as a switching tower at the intersection with the San Antonio & Aransas Pass line. Texas began its numbering system for rail switching towers in 1901 and Flatonia's was number three after that date. It remained in active service from its construction until 1996 when it was decommissioned by Southern Pacific, shortly before the company's takeover by Union Pacific, and by that time it was the last of its kind still opereating in Texas. It was moved to its present location to save it from destruction. It is now owned by the E.A. Arnim Archives & Museum of Flatonia and open for viewing by rail fans through the Central Texas Rail History Center of Flatonia.