Illinois Route 84 (Route 84 or IL 84) is a long state highway that runs along the Mississippi River in northwestern Illinois. Illinois 84 runs from south of Green Rock (now Colona) at U.S. Route 6 to the Wisconsin state line at Highway 80 by Hazel Green, Wisconsin. Illinois 84 is 93.93 miles (151.17 km) long.

Illinois Route 84 begins at an intersection with U.S. Route 6 (US 6) south of Colona in Henry County. From US 6, it heads north into the Green Rock neighborhood of Colona, crossing the Hennepin Canal on the south side of town. Colona and Green Rock were separate communities, but in 1997, became the first communities in Illinois to merge. Route 84 curves to the west, becomes a four-lane road, and crosses the Rock River into Rock Island County.

Near the TPC at Deere Run golf course, the route turns to the north towards Carbon Cliff. It curves gently to the northwest where it meets the Route 5 and Route 92 expressway at a partial cloverleaf interchange. Route 92 joins Route 84 and they travel together through Silvis for 1+1⁄2 miles (2.4 km) before Route 84 splits off to the north in East Moline.

Continuing north, IL 84 is now following the Great River Road. It passes Campbell's Island and passes through Hampton. Southeast of Rapids City is the interchange with Interstate 80. Due to the proximity of the Mississippi River, the interchange is a partial cloverleaf, as a diamond interchange would extend over the river. The route follows the bend in the river north through Rapids City and Port Byron.

North of Port Byron, IL 84 travels to the north-northeast towards Cordova. Three miles (4.8 km) north of Cordova, the highway separates the Cordova Dragway Park to the east and the Quad Cities Nuclear Generating Station, operated by Exelon, to the west. Between the nuclear plant and Albany lies a small industrial area bordered by the Mississippi River. Across the road lies irrigated crop land of Rock Island and Whiteside Counties.

This section needs expansion. You can help by adding to it. (December 2010)

In 1924, SBI Route 84 was originally what is now Illinois Route 92, Illinois Route 192 and Illinois Route 94 from near Muscatine, Iowa to U.S. Route 67. This was dropped in 1939.

In 1955, Illinois 84 was applied on a former alignment of U.S. Route 6. In 1964, Illinois 84 arrived at its current terminus, replacing then Illinois Route 80 north to Galena due to construction of Interstate 80 through the Quad Cities.

County	Location	mi	km	Destinations	Notes
Henry	Colona Township	0.0	0.0	US 6 (Grand Army of the Republican Highway) – Geneseo, Moline
Rock Island	Carbon Cliff	5.3	8.5	IL 5 / IL 92 east to I-80 / I-88 (Ronald Reagan Memorial Highway) – Sterling, Rock Falls	Interchange; southern end of IL 92 overlap
	East Moline	6.7	10.8	IL 92 west / Great River Road (National Route) south (18th Avenue) – Moline, Rock Island	Northern end of IL 92 overlap; southern end of Great River Road overlap
	Hampton Township	12.6	20.3	I-80 – Des Moines, Joliet	I-80 exit 1
Whiteside	Fulton	35.9	57.8	US 30 – Clinton, IA, Morrison
		37.3	60.0	Lincoln Highway west (16th Avenue)	Southern end of Lincoln Highway overlap
		37.4	60.2	IL 136 / Lincoln Highway east – Fulton, Clinton, IA	Northern end of Lincoln Highway overlap
Carroll	Savanna	54.1	87.1	US 52 east / IL 64 east	Southern end of US 52 / IL 64 overlap
		56.1	90.3	US 52 west / IL 64 west (Savanna-Sabula Bridge) – Sabula	Northern end of US 52 / IL 64 overlap
Jo Daviess	Elizabeth Township	74.4	119.7	US 20 east (Ulysses S. Grant Memorial Highway) – Elizabeth, Stockton	Southern end of US 20 overlap
	Rawlins Township	89.7	144.4	US 20 west (Ulysses S. Grant Memorial Highway) / Great River Road (National Route) north – Dubuque	Northern end of US 20 / Great River Road overlap
	Vinegar Hill Township	93.8	151.0	WIS 80 north – Hazel Green
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus