Mound City is the original home of the Jayhawkers.
The origin of the term "Jayhawker" is uncertain. During the Civil war the members of the Seventh Kansas regiment, commanded by Col. C. R. Jennison, became known as "Jayhawkers", and probably from this fact the jayhawker came to be regarded by many as purely a Kansas institution, and in more recent years the term "Jayhawker" is applied to Kansas men and products, much as the word "Hoosier" is applied to a resident of Indiana, the word "Sooner" is applied to citizens of Oklahoma, or the word "Buckeye" to a resident of Ohio. But there is plenty of evidence that the word was in use long before the outbreak of the Civil War.
In 1849 a party of gold seekers from Galesburg, Illinois, bound overland for California, took the name of jayhawkers. Adjutant-General Fox (corroborated by other members of the Galesburg party) said the name was coined on the Platte River in that year, and offered the following explanation of how it was adopted: "Some kind of hawks, as they sail up in the air reconnoitering for mice and other small prey, look and act as though they were the whole thing. Then the audience of jays and other small but jealous and vicious birds sail in and jab him until he gets tired of show life and slides out of trouble in the lower earth. Now, perhaps this is what happens among fellows on the trail—jaybirds and hawks enact the same role, pro and con—out of pure devilment and to pass the hours of a long march. At any rate, ours was the crowd that created the word 'jayhawker' at the date and locality above stated ... So far as Kansas is concerned, the word was borrowed or copied; it is not a home product."
While the Civil War-era meaning of the term originated during the Bleeding Kansas Affair, Civil War jayhawkers are to be distinguished from Free State Jayhawkers who fought during Bleeding Kansas, which occurred in the decade leading up to the Civil War. Some Civil War jayhawkers had in fact supported Kansas' admission to the union as a slave state, and had fought on the opposite side from the Free-Staters during the earlier conflict. Some of their organizers, such as James H. Lane (R), were nonetheless prominent abolitionist politicians. As is often the case in insurgencies, the conflict between bushwhackers and jayhawkers rapidly escalated into a succession of atrocities committed by both sides.

Well-known jayhawkers include Lane and Charles "Doc" Jennison. Jennison's vicious raids into Missouri were thorough and indiscriminate, and left five counties in western Missouri wasted, save for the standing brick chimneys of the two-storey period houses, which are still called "Jennison Monuments" in the areas. Lane and his band of militants wore red gaiters, earning them the nickname "Redlegs", or "Redleggers". This moniker was often used interchangeably with the term "jayhawkers," although it was sometimes used to refer specifically to jayhawkers who refused to join units officially sanctioned by the U.S. Army. Guerrillas on both sides of the Missouri-Kansas border achieved some measure of legitimacy through sanction from the Federal and Confederate governments, and the bands who scorned such sanction were typically even more vicious and indiscriminate in their methods than their bureaucratically recognized counterparts. Even within Kansas, the jayhawkers were not always popular because, in the absence of federal support, they supplied themselves by stealing horses and supplies from farmers.
Jayhawker bands waged numerous invasions of Missouri and also committed some of the most notorious atrocities of the Civil War, including the Lane-led massacre at Osceola, Missouri, in which the entire town was set aflame and at least 9 of the male residents killed. The sacking of Osceola inspired the 1976 film The Outlaw Josey Wales, directed by and starring Clint Eastwood. Jayhawkers also were accused of engineering the collapse of a jail in Kansas City in which female relatives of bushwhackers were incarcerated by Union sympathizers because of their connection to pro-Confederate guerrillas.