Rock Island County is a county located in the U.S. state of Illinois, bounded on the west by the Mississippi River. According to the 2010 census, it had a population of 147,546. Its county seat is Rock Island; its largest city is neighboring Moline. Rock Island County is one of the four counties that make up the Davenport-Moline-Rock Island, IA-IL Metropolitan Statistical Area.


Rock Island County was formed in 1831 out of Jo Daviess County. It was named for Rock Island, an island in the Mississippi River now known as Arsenal Island. The Rock River (which the Sauk and Fox Indians called Sinnissippi meaning "rocky waters") flows from Whiteside County and points further east and north and joins the Mississippi River at Rock Island. The Sinnissippi Mounds, dating from the Hopewell period and on the National Register of Historic Places are upriver at Sterling in Whiteside County.


According to the U.S. Census Bureau, the county has a total area of , of which is land and (5.2%) is water.

Climate and weather

In recent years, average temperatures in the county seat of Rock Island have ranged from a low of in January to a high of in July, although a record low of was recorded in February 1996 and a record high of was recorded in July 2006. Average monthly precipitation ranged from in January to in June.

Major highways

* Interstate 74 * Interstate 80 * Interstate 88 * Interstate 280 * U.S. Highway 6 * U.S. Highway 67 * U.S. Highway 150 * Illinois Route 2 (formerly) * Illinois Route 5 * Illinois Route 84 * Illinois Route 92 * Illinois Route 94 * Illinois Route 110 * 20px Illinois Route 192

Adjacent counties

* Clinton County, Iowa (north) * Whiteside County (northeast) * Henry County (southeast) * Mercer County (south) * Louisa County, Iowa (southwest) * Muscatine County, Iowa (west) * Scott County, Iowa (northwest)

National protected area

* Upper Mississippi River National Wildlife and Fish Refuge (part)


As of the 2010 United States Census, there were 147,546 people, 61,303 households, and 38,384 families residing in the county. The population density was . There were 65,756 housing units at an average density of . The racial makeup of the county was 81.6% white, 9.0% black or African American, 1.6% Asian, 0.3% American Indian, 4.4% from other races, and 3.0% from two or more races. Those of Hispanic or Latino origin made up 11.6% of the population. In terms of ancestry, 25.9% were German, 14.2% were Irish, 8.7% were English, 6.8% were Swedish, and 5.2% were American. Of the 61,303 households, 29.0% had children under the age of 18 living with them, 45.3% were married couples living together, 12.7% had a female householder with no husband present, 37.4% were non-families, and 31.6% of all households were made up of individuals. The average household size was 2.34 and the average family size was 2.93. The median age was 40.0 years. The median income for a household in the county was $46,226 and the median income for a family was $58,962. Males had a median income of $42,548 versus $31,917 for females. The per capita income for the county was $25,071. About 8.7% of families and 12.3% of the population were below the poverty line, including 19.0% of those under age 18 and 7.1% of those age 65 or over.


At one time Mississippi Valley Airlines had its headquarters in Quad City Airport in the county. John Deere is headquartered in Moline.



* East Moline * Moline * Rock Island * Silvis


* Andalusia * Carbon Cliff * Coal Valley (part) * Cordova * Hampton * Hillsdale * Milan * Oak Grove * Port Byron * Rapids City * Reynolds (part)

Census-designated places

* Coyne Center * Rock Island Arsenal

Unincorporated communities

* Buffalo Prairie * Campbell's Island * Castle Junction * Edgington * Ginger Hill * Illinois City * Joslin * Taylor Ridge


Rock Island County is divided into eighteen townships: * Andalusia * Blackhawk * Bowling * Buffalo Prairie * Canoe Creek * Coal Valley * Coe * Cordova * Drury * Edgington * Hampton * Moline * Port Byron * Rock Island * Rural * South Moline * South Rock Island * Zuma


Before 1932, Rock Island County was a Republican stronghold in presidential elections, backing the party's candidate in every election from 1892 to 1928. From 1932 on, it has consistently backed Democratic Party presidential candidates outside of four national Republican landslides. In 2016, Donald Trump managed to keep Hillary Clinton to a single-digit margin of victory, the first Republican to do so since Ronald Reagan in 1984; in 2020, Joe Biden increased the Democratic margin from 8.3% to 12.1%. Due to the dominance of the Democratic Party in county politics, Rock Island County remains one of the most Democratic counties in downstate Illinois. Since 2010 the Republican Party began making inroads in county politics, gaining a few seats on the Democratic-dominated county board; however, since 2018, the Republican Party influence on the board has begun to decrease as the county resumed heavy Democratic voting.https://www.rockislandcounty.org/PreviousElections/

See also

* National Register of Historic Places listings in Rock Island County, Illinois * Quad Cities International Airport


Further reading

''Portrait and Biographical Album of Rock Island County, Illinois: Containing Full-Page Portraits and Biographical Sketches of Prominent and Representative Citizens of the County, Together with Portraits and Biographies of All the Governors of Illinois, and of the Presidents of the United States; Also Containing a History of the County, from its Earliest Settlement to the Present Time.''
Chicago: Biographical Publishing Co., 1885.

External links

Official county website

Rock Island County Historical Society
{{Coord|41.47|-90.57|display=title|type:adm2nd_region:US-IL_source:UScensus1990 Category:Illinois counties Category:1831 establishments in Illinois Category:Populated places established in 1831 Category:Quad Cities Category:Illinois counties on the Mississippi River