The original plats of Waterloo, filed in 1854, labeled this block as a "Public Square," Block 29 in the Village of Waterloo, West. It remained, in fact, in the name of the original owners, Charles and America Mullan, who deeded it to the state in 1855 as a site for a new Black Hawk County courthouse. This offer may have contributed to Waterloo's successful bid for the county seat.

When Waterloo was chosen as county seat, however, it was originally planned that the courthouse would be located in Waterloo, East on Block 38, the site of the present Lincoln Park. After a series of political maneuvers, the courthouse was finally built on 10th Street in Waterloo, East. Block 29 was returned to the Mullans by the state in 1857. They deeded it to the city in 1864 for $450 as a "Public Square and a pleasure ground for the use and benefit of all the people of Waterloo."

Under the tax laws in force at the time, however, the block was taxed as private property by Waterloo, West. Rensselaar Russell purchased Block 29 at a tax sale in 1871 in 1871, who subsequently deeded it to Waterloo for a consideration of $13.40.

Washington Park is an important part of the downtown Waterloo landscape, an open space that survives as a vestige of pioneer Waterloo in the midst of a modern city.