Marquette County is a county located in the U.S. state of Wisconsin. As of the 2020 census, the population was 15,592. Its county seat is Montello. The county was created in 1836 from the Wisconsin Territory and organized in 1848.

Montello is a city in and the county seat of Marquette County, Wisconsin, United States. The population was 1,495 at the 2010 census. The Fox River flows through the city. Montello is home to the largest tree in Wisconsin. A notable attraction in the city is the former granite quarry, which has been transformed into a park with several waterfalls.