Indigenous peoples lived along the Mississippi River and related waterways for thousands of years before European contact.

This early agricultural community quickly produced a surplus, and grains were sold to the lower Louisiana colony for years.

Beginning on the Mississippi River where the base line, which is about three-fourths of a mile below Judge Briggs's present residence, strikes the said river; thence with the base line until it strikes the first township line therefrom; thence southeast to the southeast corner of township two south, range nine west; thence south to the southeast corner of township four north, range nine west; thence southwestwardly to the Mississippi, so as to include Alexander McNabb's farm, and thence up the Mississippi to the beginning shall constitute a separate county, to be called MONROE.

Illinois Territorial Laws 1815-16, p. 25[3]It was named in honor of James Monroe,[4] who had just served as United States Secretary of War and who was elected President later that same year.

Its first county seat was Harrisonville, named for William Henry Harrison, former governor of the Northwest Territory and future President.

Harrison invested in several tracts of land in the American Bottoms above Harrisonville, mostly in the present precinct of Moredock, ownership of which he retained until his death.

[7] The strip of Precinct 6 from the survey township line east to the Kaskaskia was added, once again from St. Clair, two years later in 1827.

The transition zone between has high bluffs of limestone and dolomite and has distinctive Karst topography with numerous sinkholes, caves, and springs.

which crosses them several times, through old Valmeyer and Fults on past Prairie du Rocher in Randolph County.

Since that time, however, the county has become predominately Republican, and the only Democrats to gain a majority since 1904 have been Catholic Al Smith in 1928, Franklin D. Roosevelt in 1932 and 1936, and Lyndon Johnson in 1964.

Since 1968, Monroe County has been carried by the Republican Presidential nominee in every election except when Bill Clinton won a narrow plurality in 1992.