Rockford is a city in Winnebago County, Illinois, United States. Located in the far northern part of the state on the banks of the Rock River, Rockford is the county seat of Winnebago County (a small portion of the city is located in Ogle County). The largest city in Illinois outside of the Chicago metropolitan area, Rockford is the fifth-largest city in the state and the 171st most populous in the United States. In the 2020 census, Rockford had a population of 148,655 anchoring the Greater Rockford Metropolitan Area with a population of 348,360.

Settled in the mid-1830s, the position of the city on the Rock River made its location strategic for industrial development. During the second half of the 19th century, Rockford was notable for its output of heavy machinery, hardware and tools; by the 20th century, it was the second leading center of furniture manufacturing in the nation, and 94th largest city. During the second half of the 20th century, Rockford struggled alongside many Rust Belt cities. Since the late 1990s, efforts in economic diversification have led to growth of automotive, aerospace, and healthcare industries, as well as the undertaking of various tourism and downtown revitalization efforts.

Nicknamed the Forest City, Rockford is presently known for various venues of cultural or historical significance, including Anderson Japanese Gardens, Klehm Arboretum, Tinker Swiss Cottage, the BMO Harris Bank Center, the Coronado Theatre, the Laurent House, and the Burpee Museum of Natural History. Its contributions to music are noted in the Mendelssohn Club, the oldest music club in the nation, and performers such as Phantom Regiment and Cheap Trick. Notable outdoor or recreational spots near Rockford are Rock Cut State Park, Atwood Homestead County Forest Preserve, and Lowden State Park.