Early years

Mercer County was organized February 14, 1845, from part of Grundy County.^[3] It is named in honor of General Hugh Mercer, who fought and died in the American Revolutionary War. The first permanent settlements in what is now Mercer County were in 1837, when a few families from other parts of Missouri moved to the area. James Parsons, a Tennessee native, is generally considered to be the first permanent settler, in the spring of 1837.^[4] The land was still included as part of Livingston County at that time and would remain so until 1841 when it would become part of the newly created Grundy County. Prior to 1837, the land was used by Native American tribes, primarily the Sac/Fox and Potawatomi, as prime hunting grounds. The occasional temporary hunting village would be established by the tribes; otherwise, the land was devoid of humans. The town of Princeton, named for the battle where General Mercer was killed, was established as the county seat in 1847.^[5] The northern boundary of the county was in dispute for the first six years of its existence due to the Honey War, a bloodless territorial dispute between Missouri and Iowa. The boundary was 9.5 miles farther north than present day prior to an 1851 decision by the U.S. Supreme Court.

Civil War

Mercer County, like its neighbor to the east Putnam County, was a staunch supporter of the Union. Most county residents had roots in northern U.S. states "back east" like Pennsylvania, Ohio, and Indiana, and did not have the strong slave-holding tradition of other northern Missouri counties like Macon, Audrain, and Monroe (commonly referred to as Little Dixie), whose population largely emigrated from Southern states. In the 1860 U.S. Census, only 12 Mercer County families were listed as slave owners, with a combined total of 24 slaves.^[6] Fewer than 20 Mercer County men fought for the Confederacy, while well over 1,000 volunteered for Union service. Among the units containing men from Mercer County were the 23rd, 27th and 35th Regiments, the 2nd and 12th Cavalry, the 5th Kansas Cavalry, and various smaller units of the Missouri State Militia.^[7] The 44th Missouri Infantry (USA), consisting of men from Mercer, Grundy, Sullivan, and other northwest Missouri counties, served a pivotal role in the Union victory at the Battle of Franklin, TN, on November 30, 1864.

Adjacent counties

• Decatur County, Iowa (northwest)
• Wayne County, Iowa (north)
• Putnam County (east)
• Sullivan County (southeast)
• Grundy County (south)
• Harrison County (west)

Major highways

• U.S. Route 65
• U.S. Route 136

2020 Census

Public libraries

• Mercer County Library^[17]

Cities

• Mercer
• Princeton (county seat)

Village

• South Lineville

Census-designated place

• Ravanna

Other communities

• Mill Grove
• Modena

Historical communities

Source^[18]

Local

The Republican Party predominantly controls politics at the local level in Mercer County. Republicans hold all of the elected positions in the county. In the 2020 presidential election, Mercer County had the highest Republican turnout in the state of Missouri with greater than 86% of the population voting for Donald Trump.

State

All of Mercer County is a part of Missouri's 3rd District in the Missouri House of Representatives and is represented by Danny Busick (R-Newtown).

All of Mercer County is a part of Missouri's 12th District in the Missouri Senate and is currently represented by Dan Hegeman (R-Cosby).

Federal

All of Mercer County is included in Missouri's 6th Congressional District and is currently represented by Sam Graves (R-Tarkio) in the U.S. House of Representatives.