The construction of the Rock Island Armory began with a ground breaking by Governor Henry Horner on March 8, 1936. The building was designed by Benj. A. Horn, a prominent Rock Island architect. The general contractor for the Armory was Coath & Goss of Chicago. It was built at a cost of $400,000, made possible through the national building program and the Public Works Administration (PWA). The Armory was to be the headquarters of two National Guard units and the Rock Island Naval Reserve.

The monolithic steel reinforced concrete structure is 232 feet long, 148 feet wide, and 65 feet high with a total area of approximately 80,000 square feet and is three stories tall. The free-span barrel vaulted roof is supported by eight steel girders weighing 18 tons each and maintains a clear height of 45 feet.

The Armory was dedicated by Illinois Governor Horner on Armistice Day, November 11, 1937. The dedication was attended by more than 3,000 persons, and was preceded by a parade through the downtown district.

A unique feature of the Armory is that the structure itself is part of the massive seawall that protects Rock Island from the Mississippi River flooding. Originally, the flood wall was made of stone riprap. Following the flood of 1965, a reinforced concrete flood wall was incorporated into the building’s structure, in conjunction with the construction of an overall flood protection system for the city.

In 1996, the National Guard vacated the Armory for a new facility, and requested proposals for purchase of the building and property. The City of Rock Island submitted the only proposal, with a purchase price of $90,000. The offer was accepted with approval by Governor James Edgar in January 1997.

After much public debate, the City of Rock Island determined the highest and best use of the riverfront site was to demolish the Armory. Illinois Historic Preservation Agency approved release of the covenant (allowing the partial or complete demolition to proceed) on May 10, 2007.