Rockford is a city in Winnebago and Ogle counties in the U.S. state of Illinois. It is located in far northern Illinois on the banks of the Rock River. The fifth-most populous city in Illinois with a population of 148,655 at the 2020 census, it anchors the Rockford metropolitan area with 337,000 residents. Rockford is the county seat of Winnebago County and the most populous city in Illinois outside the Chicago metropolitan area.

Settled in the mid-1830s as Midway, Rockford became strategic for industrial development, stemming from its location roughly equidistant between Lake Michigan and the Mississippi River. During the second half of the 19th century, it became notable for its production of heavy machinery, hardware, and tools. At the beginning of the 20th century, the city was the second leading center of furniture manufacturing in the U.S. During the second half of the 20th century, Rockford struggled alongside many Rust Belt cities to maintain its previous industrial presence. Since the late 1990s, efforts in economic diversification have led to the growth of automotive, aerospace, and healthcare industries, as well as the undertaking of various tourism and downtown revitalization efforts.

Nicknamed "the Forest City" for its heavily forested residential neighborhoods during the 20th century, Rockford is 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 U.S.^{[citation needed]}, and performers such as Cheap Trick and Phantom Regiment Drum and Bugle Corps.

Rockford traces its roots to 1834, as the combined settlements of Midway were founded on both banks of the Rock River. On the west bank, Germanicus Kent and Thatcher Blake (with his slave Lewis Lemon) founded Kentville; the east bank was settled by Daniel Shaw Haight. With the location of the Rock River equidistant between Lake Michigan and the Mississippi River, the combined settlement derived the name "Midway". In 1836, Winnebago County was created (from both Jo Daviess and LaSalle counties), with Midway named as its county seat, as it was "halfway between Galena and Chicago on a line of four-horse coaches."

In 1837, the village of Midway was renamed Rockford, highlighting a rocky river ford across the Rock River in the village. In the same year, Rockford established its first post office, with Daniel Shaw Haight as the first postmaster. In 1840, the first weekly newspaper began circulation. In 1847, Rockford Female Seminary – today Rockford University – was founded. On January 3, 1852, Rockford was officially chartered as a city; a year later the long-running "Forest City" nickname first appeared, used by the New York Tribune. Also in 1852, the Galena and Chicago Union Railroad connected Rockford to Chicago by railroad.

At the time of its founding, many of the village's residents were transplants from the Northeastern United States and upstate New York. Descended from English Puritans, the Midway/Rockford population was similar to much of the rest of northern Illinois and nearly all of Wisconsin during the mid-19th century. After the Black Hawk War, additional immigrants moved to northern Illinois; during the 1830s and 1840s, Rockford and Winnebago County were considered a cultural extension of New England.

During the antebellum period, Rockford shared abolitionist leanings, lending considerable support to the Free Soil Party and the later Republican Party. In 1848, 42 percent of voters in Winnebago County (where Rockford dominated as the county seat) voted for Martin Van Buren. In 1852, Free Soil candidate John P. Hale became the first presidential candidate to visit Rockford, although he would only receive 28 percent of the vote. In 1860, Abraham Lincoln won 3,985 votes in Winnebago County to the 817 votes of Stephen A. Douglas.

The 1850s brought industry that would change Rockford forever. In 1853, inventor John Henry Manny moved to Rockford to produce horse-drawn mechanical reapers for farmers and transport the finished products by rail. Chicago implement manufacturer Cyrus McCormick (whose company became International Harvester) took Manny to court after he produced nearly 6,000 machines; Manny would prevail on both judgement and an appeal. Along with the production of agricultural machines, Swedish furniture cooperatives established the city as a manufacturing base. The Rockford Union Furniture Company, under John Erlander, spearheaded these cooperatives. Today, Erlander's home is a Rockford museum that shows his efforts in elevating Rockford to second in furniture manufacturing in the United States, behind Grand Rapids.