Settled in the mid-1830s, the position of the city on the Rock River made its location strategic for industrial development.

Early settlers called it "Forest City" because of the river valley's verdant woods, but in the late 1950s, Rockford lost over 50,000 trees to Dutch elm disease, thinning the tree canopy for decades. Today, the city has 7,000 acres of parkland, tree-lined streets, an exceptionally green downtown, a riverside trail, and several magnificent public gardens.

The city's industrial background has produced many important and interesting inventions, including the Nelson knitting machine, airbrush, electric brake, electric garage door opener, dollar bill changer, and electronic dartboard.

During the existence of the All American Girls Professional Baseball League from 1944 to 1954, the city supported the Rockford Peaches, the team featured in the 1992 movie A League of Their Own.

Rockford traces its roots to 1834, when Germanicus Kent, Thatcher Blake, and Lewis Lemon founded Kentville on the west bank of the Rock River and Daniel Shaw Haight founded a settlement on the east bank. The combined settlement was initially called Midway due to the fact that the Rock River was equidistant between Lake Michigan and the Mississippi River. It was renamed Rockford in 1837.

Much to Rockford's chagrin, it was once known as the "Screw Capital of the World" because of the billions of screws, bolts, and fasteners its factories produced for the manufacturers of the world.

While its congressional district favored Republicans, Rockford continuously elected former Socialists as mayor between 1921 and 1955.

In 1980, then Congressman John B. Anderson, representing the 16th Congressional District in Illinois which includes Rockford, ran an independent campaign for president, receiving 6.6% of the popular vote.

In 1963, the Rockford area was selected by Chrysler Corporation to construct an assembly plant. While not located directly in the city, the Chrysler assembly plant quickly became the largest employer in the region.

Boxer Sammy Mandell (born Salvatore Mandala) was known as the "Rockford Sheik" due to his Rudolph Valentino like good looks and as the "Rockford Flash" due to his fast hands and foot speed. On July 3, 1926, he outlasted Rocky Kansas to win the World Lightweight Boxing Championship in a fight that lasted 10 rounds in the pouring rain in front of 20,000 fans at Comiskey Park. Mandell successfully defended his crown against four contenders, including future champions Tony Canzoneri and Jimmy McLarnin, and is ranked by the statistical boxing website BoxRec as the 13th greatest lightweight boxer in the history of the sport.