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. The Montello post office was established in 1850, and still operates today with the zip code 53949.