The Old Post Office (NRHP-listed as Watertown Post Office) is a historic building located at 26 South Broadway in Watertown, South Dakota.

The Watertown Post Office was built in 1908 and served until 1976[citation needed].

From 1976 to 2009, it was known as Old Post Office Square, and housed several tenants.

[3] The building was added to the National Register of Historic Places in 1976.

This article about a property in South Dakota on the National Register of Historic Places is a stub.