Since that time, the post office has served the general area and has always carried the name of Calumet. A branch of this office was opened in Laurium on February 28, 1895 and discontinued operation December 31, 1935. The Laurium Post Office then became a Contract Branch of Calumet on January 1, 1936.

At some point before the 1890s, the Calumet Post Office was moved nearer to the Red Jacket commercial district. In the 1890s it occupied space in the Union Building at the corner of Fifth Street and Red Jacket Road. The post office appears to have operated out of a number of buildings in the intervening decades.

By 1930, the office was located at 113 Fifth Street. The present Post Office Building at Sixth and Portland Streets was completed in 1939 as part of the Works Progress Administration's federal building program. The location of this important public building reinforced Sixth Street's civic function. Designs for the building were provided by Louis A. Simon, the U.S. Postal Service's Supervising Architect. The one-story rectangular structure rests on a poured concrete base. Walls are tan-colored brick veneer; the cornice is dolomite. A notable decorative element is the polished aluminum eagle (now painted) that fills a window above the central entrance.

In the building's public lobby is a mural depicting copper mining that was commissioned by the Public Buildings Administration's Section of Fine Arts. Entitled "Copper Mining in Calumet" the mural was painted by Joseph A. Lasker, an artist who received the mural commission through a Section of Fine Arts national competition. Submitted by: Paul E. Petosky