Grundy County
Also known as Grundy County, Illinois, Grundy County, IL
county in Illinois, United States
Key facts
- Country
- United States
- State
- Illinois
- Founded
- February 17, 1841
- Named after
- Felix Grundy
- Seat
- Morris
- Largest city
- Morris
- Total
- 430 sq mi (1,100 km )
- Land
- 418 sq mi (1,080 km )
- Water
- 12 sq mi (31 km ) 2.9%
- Estimate 2025
- 54,052
- Density
- 126/sq mi (48.5/km )
- Time zone
- UTC−6 ( Central )
- Summer dst
- UTC−5 ( CDT )
~7 min read
Article
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.