The Salt Lake City and County Building was completed in 1894. It was finished after years of controversy and a constantly increasing cost which ended at $900,000. Talk of combining both Salt Lake City Hall and the Salt Lake County Courthouse had begun in the 1880s. Both were in small structures that were becoming overcrowded. By 1889, plans for a "Joint Building" costing $150,000 had been made. On the first week of February 1890, excavation started on the southwest corner of 100 South and 200 East. Later that month, a new and non-Mormon city administration took office and halted the project. For three months, the new administration held that the Joint Building was an extravagent project before deciding to continue construction. In November 1890, construction was halted once again when the original architect, C. E. Apponyi, was fired. By this time, cost estimates for the building had doubled and the issue was deadlocked in the City Council with Mormons and non-Mormons being at odds. The City Council finally decided to start on a new building located at the center of the Eighth Ward Square, soon known as Washington Square. Several people criticized the location, which was felt by many to be too far from the city center, but the project went forward anyway. The City Council sent notices to architectural firms in Salt Lake, Denver, San Francisco, and Chicago for competing designs. The project was to not exceed $350,000. The winning architect was the firm of Monheim, Bird, and Proudfoot of Salt Lake City. Their design raised considerable controversy concerning the size and expense of the building.

The bid for the contractor also had a hurdle, the contractor chosen was the firm of John H. Bowman whose bid of $377,978 was the third lowest. However, Bowman's firm was the only one that had labor union support and therefore was the one chosen. Construction began in the Spring of 1892. The Joint Building's troubles continued when the Panic of 1893 reduced the revenue of Salt Lake City and Salt Lake County. Once more, work was halted until the two governments could find a way to make the building less expensive. After a few months, fourteen stained-glass windows were dropped from the project and the workforce was downsized. Finally, in November 1894, the building was substantially finished and was dedicated the next month. Although the building had been very expensive and had suffered many setbacks, it was used very frequently. Utah's Constitutional Convention was held in the Joint City and County Building in 1895 and when Utah was admitted to the Union as a state in 1896, the City and County Building became Utah's first capitol. For several years the building was used by the city, the county, and the state. Salt Lake City Hall was located in the North wing of the building and the County Courthouse was located in the South wing. It was in this South wing that the murder trial of Labor Leader Joe Hill was held in 1914. The state legislature and the governor also used the building until 1915 when Utah's current capitol building was finished.

After nine decades of extensive use by city and county, the building was in disrepair and some considered levelling it. Instead, it was decided to move Salt Lake County offices to another location and rennovate the building for use by Salt Lake City. Architects Burtch W. Beall Jr. of Salt Lake City and Ehrenkrantz Group of San Francisco supervised the $30.3 million project. The three-year project began in 1986 and included placing the building on base isolaters to absorb seismic shocks during an earthquake. In 1989, the building opened with a three-day celebration. Washington Square was also the site of celebrations in 1995 when Salt Lake City received the Olympics, and in the following years for Utah's Centennial and Salt Lake City's Sesquicentennial. Washington Square was also a popular site during the 2002 Winter Olympics.