[3][4] The Harrisonville area was long inhabited by speakers of the Dhegihan Siouan-language family: The Osage, Quapaw, Omaha, Ponca and Kansa tribes make up this sub-group.

The Kansa tribal range extended southward from the Kansas-Missouri River junction as far as the northern edge of present-day Bates County, Missouri, taking in the sites of modern Pleasant Hill, Garden City, Archie and Drexel.

Other Lenape had previously migrated south to Texas, seeking refuge in what was still Mexican territory after it gained independence from Spain.

Lackey was considered a "squatter," as he built a cabin and enclosed a small field on the tract of public land taken to establish the county seat.

William Lyon was appointed clerk of the court and county government was organized, including the establishment of Grand River Township.

In the spring of 1837 the town of Harrisonville was platted by Enoch Rice, Francis Prine and Welcome Scott, who had been appointed commissioners by the state legislature in the winter of 1836.

These commissioners, in company with Martin Rice, the county surveyor, met at the home of John Cook on April 3, 1837, to resolve Lackey's preemption claim.

Within these 160 acres (0.65 km2) there were to be four streets: Wall and Pearl running east to west, and Lexington and Independence going north and south, each less than 40 feet wide.

In 1857 Cass County had approved a large stock subscription for the Pacific Railroad Company, to support its construction in the area.

At the time of the shootings, a related mob burned a Republican newspaper owned by Porter J. Coston, in Harrisonville, Missouri.

In 1863 the town was depopulated, as the United States forces pushed the people out in an effort to reduce any local support for insurgent guerrilla activity in the area.

The most predominant denominations among residents in Cass County who adhere to a religion are Southern Baptists (43.71%), Roman Catholics (17.42%), and United Methodists (11.07%).

Cass County, along with the rest of the state of Missouri, is represented in the U.S. Senate by Josh Hawley (R-Columbia) and Roy Blunt (R-Strafford).

Voters in Cass County generally adhere to socially and culturally conservative principles which tend to influence their Republican leanings.

On the Democratic side, former Vice President Joe Biden (D-Delaware) both won statewide and carried Cass County by a wide margin.

Incumbent President Donald Trump (R-Florida) faced a primary challenge from former Massachusetts Governor Bill Weld, but won both Cass County and statewide by overwhelming margins.

Businessman Donald Trump (R-New York) narrowly won the state overall, but Senator Ted Cruz (R-Texas) carried a plurality of the vote in Cass County.

Senator Rick Santorum (R-Pennsylvania), who finished first in the state at large, but eventually lost the nomination to former Governor Mitt Romney (R-Massachusetts).

In 2008, the Missouri Republican Presidential Primary was closely contested, with Senator John McCain (R-Arizona) prevailing and eventually winning the nomination.

Then-Senator Hillary Clinton (D-New York) received more votes than any candidate from either party in Cass County during the 2008 presidential primary.

Despite initial reports that Clinton had won Missouri, Barack Obama (D-Illinois), also a Senator at the time, narrowly defeated her statewide and later became that year's Democratic nominee, going on to win the presidency.