It is named for Felix Grundy, a US Attorney General. The seat and largest city are both Morris, located on the Illinois River.
The area is also known for its coal, attracting miners from Pennsylvania.
It borders Kendall, Will, Kankakee, Livingston and La Salle Counties.
Main Highways include I-55, I-80, US-6 IL-47 and IL-113.
Seneca Lift Bridge