Grundy County, Illinois

Grundy County
County
Grundy County Courthouse
Flag Seal
Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 41°17′N 88°26′W / 41.29°N 88.43°W / 41.29; -88.43
Country	United States
State	Illinois
Founded	February 17, 1841
Named for	Felix Grundy
Seat	Morris
Largest city	Morris
Area
• Total	430 sq mi (1,100 km2)
• Land	418 sq mi (1,080 km2)
• Water	12 sq mi (30 km2)  2.9%
Population  (2020)
• Total	52,533
• Density	120/sq mi (47/km2)
Time zone	UTC−6 (Central)
• Summer (DST)	UTC−5 (CDT)
Congressional district	16th
Website	www.grundyco.org

Grundy County is a county in the U.S. state of Illinois. According to the 2020 census, it has a population of 52,533.^[1] Its county seat is Morris.^[2]

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.^[3]

Illinois's state fossil, the unique and bizarre Tully Monster, was first found in Mazon Creek. Grundy County is 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.