Beloit is a city in Rock County, Wisconsin, United States. As of the 2020 census, the city had a population of 36,657 people. Beloit is a princip…Beloit is a city in Rock County, Wisconsin, United States. As of the 2020 census, the city had a population of 36,657 people. Beloit is a principal city of the Janesville–Beloit metropolitan statistical area and is included in the Madison–Janesville–Beloit combined statistical area.