Grundy County is a county in the U.S. state of Illinois. According to the 2010 census, it has a population of 50,063. Its county seat is Morris.Grundy County is part of the Chicago-Naperville-Elgin, IL-IN-WI Metropolitan Statistical Area.
In 2010, the center of population of Illinois was in Grundy County, just northeast of the village of Mazon.Illinois's state fossil, the unique and bizarre Tully Monster, was first found in Mazon Creek. Grundy County Speedway is located in Morris. Grundy County is also home to Dresden Generating Station—the first privately financed nuclear power plant built in the United States—and the Morris Operation—the only de facto high-level radioactive waste storage site in the United States.
Coordinates 41°21'26.114" N -88°25'16.243" E