The Old Customs House, also called the Old Post Office, is a historic building located at the corner of Clinch Avenue and Market Street in Knoxville, Tennessee, United States.

[5] Construction of the original portion of the Customs House (at the corner of Clinch and Market), designed by U.S. government chief architect Alfred B. Mullett (1834–1890), began in 1871 and was completed in 1874.

[6] As Knoxville's population quadrupled in the late 19th century, the increased postal activity left the Customs House critically overcrowded,[6] and the building was enlarged in 1910.

[8] Knoxville's continued growth rendered the Customs House insufficient for the city's postal needs, and a new post office was built on Main Street in 1934.

[11] In 2004, a BarberMcMurry-designed eastern extension to the Customs House was completed, extending the structure the length of Clinch Avenue from Market to Gay Street.