Native Americans were the first to live in what became Pierce County, as evidenced in the burial mounds near Diamond Bluff.

In 1840, St. Croix County covered a large portion of northwest Wisconsin Territory.

The racial makeup of the county was 92.3% White, 1.0% Black or African American, 0.7% Asian, 0.5% Native American, 1.1% from other races, and 4.3% from two or more races.

As of the census[12] of 2000, there were 36,804 people, 13,015 households, and 9,032 families residing in the county.

The racial makeup of the county was 98.01% White, 0.25% Black or African American, 0.29% Native American, 0.43% Asian, 0.03% Pacific Islander, 0.28% from other races, and 0.72% from two or more races.

21.30% of all households were made up of individuals, and 7.50% had someone living alone who was 65 years of age or older.