The old post office of New Braunfels was built during the full-scale 20th century transformation of the United States Postal System. Programs like the United States Postal Savings System, parcel post, airmail, and improved rural delivery services expanded the reach and popularity of the postal system for letters and packages. In 1915, President Woodrow Wilson signed an act to fund the construction of a postal office building in New Braunfels. Prior to this, the postal service had its headquarters in various homes and businesses. The new building was dedicated in 1915, with the names on the cornerstone of William G. McAdoo, U.S. Secretary of the Treasury responsible for post offices, and James A. Wetmore, supervising architect. Many contractors were involved in construction, with Round Rock Limestone and D'Hanis and Acme Brick companies as suppliers for much of the exterior materials.
During the Great Depression and World War II, the office also sold war bonds and handled food stamps and ration books. In the 1960s, the office was remodeled and an addition to the north side was constructed. The location of the New Braunfels Post Office was eventually moved to Seguin Avenue in 1985. For 70 years, the New Braunfels community was supported and served through this post office building. In 2007-08, the building was completely renovated
to house McAdoo's Seafood Company, named for the former Secretary of the Treasury.