Grundy County, Illinois
Grundy County is located in the U.S. state of Illinois. According to the 2020 census, it has a population of 52,533. Its county seat is Morris.
Grundy County is part of the Chicago metropolitan area.
In 2010, the center of population of Illinois was in Grundy County, just northeast of the village of Mazon.
Illinois's state fossil is the Tully Monster (Tullimonstrum gregarium), a fossil organism first discovered in the Mazon Creek fossil beds. Grundy County is home to the Dresden Generating Station, a nuclear power plant that was the first privately financed nuclear power plant built in the United States. The county is also the location of the Morris Operation, a former nuclear fuel storage facility that has been described as the only de facto high-level radioactive waste storage site in the United States.