St. Charles gained one of its most recognizable landmarks on September 1, 1940. The building, which cost $250,000, was built on the site of the old Fixture Factory which had burned in 1929. It was yet another gift of the Baker and Norris families to the city.

The building, designed by R. Harold Zook and D. Coder Taylor, was to house administrative offices, city council chambers, and a museum. While it indeed does all this, the building is important more so for its architectural style and the elements incorporated into the building. Designed in the Art Moderne style, a style which combined artistic expression with modern machine age technology, the Municipal Building has smooth lines, flat surfaces, and little ornament. The building is constructed of a black granite base and white Georgian marble. Bands of deeply recessed windows pierce the lower two floors of the building. On the interior, the architects incorporated fluorescent tube lighting throughout. This technology was relatively new in the late 1930s.

Perhaps the most beautiful portion of the building is its eighty-four foot tall octagon tower. Stained glass windows, pierced grillwork, and a diamond shaped translucent top make the tower a scenic landmark. Originally, the tower had chimes that tolled every quarter hour. Unfortunately, they remained in working order only until the end of World War II.

While the Municipal Building remains essentially the same, there have been some changes made over the years. In the early 1990s, the building had to be updated in order to comply with the Americans with Disabilities Act, at which time, a two story structure connecting the Municipal Building with the old city building was constructed. A mural is the latest addition to the building. Added in 1998, the mural documents the history of St. Charles through depictions of significant historical figures and structures.