Merrill is a city in and the county seat of Lincoln County, Wisconsin, United States. It is located to the south of and adjacent to the Town of Merrill. The population was 9,661, according to the 2010 census. Merrill is part of the United States Census Bureau's Merrill MSA, which includes all of Lincoln County. Together with the Wausau MSA, which includes all of Marathon County, it forms the Wausau-Merrill CSA.