In 1889, after urging from Saginaw Congressman Aaron Bliss, who later became governor, Congress appropriated one hundred thousand dollars for a new federal building in Saginaw, but the project stalled for several years when city leaders rejected two sets of plans prepared by U. S. Treasury Department architects. Congressman William Linton, who represented the district from 1893 to 1897, secured a third design, and in 1897 William Aiken, the newly appointed supervising architect of the Treasury Department, submitted a final plan that local officials enthusiastically approved. On May 11, 1897, Saginaw Postmaster A. G. Wall turned the first spade of dirt in ceremonies marking the start of construction, and William Linton became Saginaw's postmaster in 1898. Inspired by Saginaw's French heritage, William M. Aiken designed the building as a stately French chateau for the city's post office, with corner towers he said reflected the defensive feature of frontier life. Opened on July 4, 1898, it was built of Bedford limestone, ornamented with copper, topped with a red slate roof, and finished inside with marble quarried in Colorado. In 1930, plans to demolish it because a larger structure was needed gave way instead to a major enlargement by Saginaw architect Carl Macomber, who doubled its size while keeping the addition compatible with the original building. In the 1970s, the county acquired the post office and rehabilitated it as the Castle Museum, and it was listed in the National Register of Historic Places in 1987.