Old St. Johns County Jail, Prison museum in St. Augustine, Florida, United States.

The Old St. Johns County Jail is a two-story building at 167 San Marco Avenue in St. Augustine, completed in 1891 by the P.J. Pauley Jail Building and Manufacturing Company of St. Louis. Its northern wing held a general population and maximum security area, a women's section and a lower-level kitchen, while the southern wing contained the sheriff's office and family living quarters. It now operates as the Old Jail Museum.

The P.J. Pauley Jail Building and Manufacturing Company of St. Louis built the jail in 1891 with $10,000 from Henry Flagler, who wanted the former jail's land for his Ponce de León Hotel. It served as the St. Johns County Jail until 1953, when facilities moved to a modern building. Entrepreneur Henry "Slim" McDaniel then turned it into a roadside attraction, and it joined the National Register of Historic Places in 1987.

Costumed guides process visitors as new prisoners, and the museum displays weapons and a pictorial history of the eight hangings, with emphasis on Sheriff C.J. Perry's years living on site with his family. The jail is also the finale of the Old Town Trolley Ghosts and Gravestones tour, which opens the building at night.

The museum is open daily and located in downtown St. Augustine. Visitors should expect narrow spaces and wear comfortable shoes, as exploring multiple levels is part of the visit.

The building had a gallows on the grounds where serious criminals were executed. This spatial arrangement, which linked punishment directly with the prison, remains visible in the site's layout today.