Calhoun County is at the tip of the peninsula formed by the courses of the Mississippi and Illinois rivers above their confluence and is almost completely surrounded by water.

[3] Calhoun County is part of the Metro-East portion of the St. Louis, MO-IL Metropolitan Statistical Area.

The southern side of the county, covered in thick forest, was untouched until the population began to expand in the late 1840s with the arrival of German immigrants.

Land was cleared for farming, exporting lumber, and constructing spacious log barns, typically 200 square feet (19 m2) in size, which were a "trademark of successful German farmers.

The long grass was trampled down and all around were strewn the relics of the hideous orgies which formed the ordinary sequel of an Iroquois victory.

O'Neal lived in Point Precinct a number of years before any other European settlers came to that region, and when they did come he refused to mingle with them.

He continued to live in this cave until his death in 1842, and after that he was referred to as "The Hermit" due to the fact that he would not visit the other settlers or allow them to come to his place.

The next settlers to come to the area were French trappers and people of mixed ancestry, who started a community about a mile above what was called the Deep Plain Ferry, on the Illinois River, in the southern part of the county.

The French settlers who lived here came sometime after 1800 and by the year 1811 there were 20 families, who had a small village on the bank of the river, and cultivated a common field of about 500 acres.

One writer said that these families were driven away by the Native Americans in 1814, but there is some doubt as to the accuracy of the statement as John Shaw who took part in battles with the natives in the region and was a community leader at the time does not mention in his writings any harm coming to the settlers at Cap au Gris.

As early pioneers continued to settle in Calhoun County there is evidence of troubled relations between the European settlers and the Native Americans.

The flood also closed all crossings over the rivers in the county including the bridge in Hardin and all ferries, leaving residents without access to groceries, gasoline, or other supplies.

The Great Flood of 1993 was devastating to Calhoun County because it destroyed homes, infrastructure, and caused many residents to leave.

In the town of Grafton, Illinois, downriver from Calhoun County, a statue was placed to mark where Marquette and Joliet are claimed to have landed during their famous exploration.

However, local historians in Calhoun County claim that the true stopping point of the expedition is a place now called "Perrin's Ledge", located several miles above Kampsville, Illinois.

Their claims seem to be much better supported by Marquette's diary where he writes, "We entered the mouth of the Illinois River very early in the morning", and further on he says: "We spent the night with some friendly Indians."

If they were traveling at a rate of slightly better than twenty-five miles a day and entered the river early in the morning (this was the last week in August) they would have been in the Kampsville area by evening.

The Golden Eagle ferry, which is privately operated and charges a toll, crosses the Mississippi River to St. Charles County, Missouri.

Only when German-Americans were offended at Woodrow Wilson's policies towards Germany did the county vote Republican for the first time in 1920, and it narrowly repeated that in the GOP landslides of 1924 and 1928.

The county did turn strongly Republican due again to opposition to war involvement in 1940, and remained Republican-leaning for three decades.

[citation needed] Between 1970 and 2008 Calhoun turned Democratic once more – George Bush senior in 1992 won a smaller proportion of the vote than Alf Landon in 1936 or William Howard Taft in 1912.

Despite Donald Trump defeating Hillary Clinton by almost 40 points in 2016, Calhoun County concurrently voted Democratic in the Senate race, narrowly supporting Tammy Duckworth over Mark Kirk.