[2] Mercer County is included in the Davenport-Moline-Rock Island, IA-IL Metropolitan Statistical Area.

In May 1812, Congress passed an act which set aside lands in Arkansas, Michigan, and Illinois as payment to volunteer soldiers in the War of 1812.

The organization of the county government was finally completed in 1835, after a large influx of settlers following the Black Hawk War.

The county never voted for a Democratic presidential candidate until Lyndon Johnson’s 1964 landslide over Barry Goldwater – the solitary break in Whig and Republican dominance occurring in 1912 when the GOP was mortally split and Progressive Theodore Roosevelt carried the county over conservative incumbent President William Howard Taft.

Between then and 2012, Mercer was solidly Democratic, but concern over declining economic opportunities in the “Rust Belt” caused a dramatic swing to populist Republican Donald Trump in 2016.

Mercer County is located in Illinois's 17th Congressional District and is currently represented by Democrat Cheri Bustos.

The county is located in the 37th district of the Illinois Senate, and is currently represented by Republican Chuck Weaver.