Rock Island County, Illinois

Rock Island County at the time of its creation in 1831

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.[4] The Rock River (which the Sauk and Fox Indians called Sinnissippi, meaning "rocky waters")[5] 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 451 square miles (1,170 km²), of which 428 square miles (1,110 km²) is land and 24 square miles (62 km²) (5.2%) is water.[6]

As of the 2010 United States Census, there were 147,546 people, 61,303 households, and 38,384 families residing in the county.[13] The population density was 345.0 inhabitants per square mile (133.2/km²). There were 65,756 housing units at an average density of 153.8 per square mile (59.4/km²).[6] 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.[13] 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.[14]

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.[13]

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.[15]

At one time Mississippi Valley Airlines had its headquarters in Quad City Airport in the county.[16] John Deere is headquartered in Moline.[17]

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, except for the national Republican landslides of 1952, 1956, 1972, and 1980. 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 outside of the Chicago area in 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.[18]

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

• 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.

• Official county website
• Rock Island County Historical Society

41.47°N 90.57°W / 41.47; -90.57