Jasper County is located in the southwest portion of the U.S. state of Missouri. As of the 2020 census, the population was 122,761. Its county seat is Carthage, and its largest city is Joplin. The county was organized in 1841 and named for William Jasper, a hero of the American Revolutionary War. Jasper County is included in the Joplin Metropolitan Statistical Area. The Jasper County Sheriff's Office has legal jurisdiction throughout the county.

Before European contact, the area that today makes up Jasper County was the domain of the Osage Native Americans, who called themselves the "Children of the Middle Waters" (Ni-U-Kon-Ska). A Siouan language tribe, they had migrated west and south centuries before from the Ohio Valley.

They were powerful and dominated a large territory encompassed the land between the Missouri and Osage rivers to the north, the Mississippi River to the east, and the Arkansas River to the south. To the west were the Great Plains, where they hunted buffalo. By the late 17th century, the Osage were calling themselves Wah-Zha-Zhe.

The earliest record of European-Osage contact is a 1673 map by French Jesuit priest and explorer Jacques Marquette. He noted the people he encountered as the Ouchage, his way of pronouncing the sound of the name with French spelling conventions. A few years after the Marquette expedition, French explorers discovered a Little Osage village and called it Ouazhigi. French transliterations of the tribe's name settled on a spelling of Osage, which was later adopted by English-speaking European Americans.

In 1682 Robert de La Salle canoed down the length of the Mississippi River to the Gulf of Mexico, claiming and naming the entire Mississippi basin as "La Louisiane" in honor of King Louis XIV. In 1699 Louisiana was designated as an administrative district of New France. The European colonists and nationals (France, England and Spain) considered this to be French territory. The French divided the Louisiana district into upper and lower parts, with the Arkansas River as the dividing line.

After France and Spain's defeat by Great Britain in the Seven Years' War in 1763, France ceded Louisiana to Spain and most of the rest of New France, on the east side of the Mississippi River, to the British. They exchanged Cuba with Spain and took over east Florida. For a few decades, the Spanish District of New Madrid, containing present-day Jasper County, was the southernmost of the five Spanish districts comprising Upper Louisiana. France regained control of Louisiana through the secret Treaty of San Ildefonso in 1800, but in 1803, following defeat of his troops in an effort to retake the colony of Saint Domingue in the Caribbean, Napoleon Bonaparte I decided to sell his North American territory to the United States in what is known as the Louisiana Purchase.

The Osage began treaty-making with the United States in 1808 with the first cession of lands in Missouri in the (Osage Treaty). The Osage moved from their homelands on the Osage River in 1808 to the Jasper County area of southwest Missouri. In 1825, the Osages ceded their traditional lands across present-day Missouri, Arkansas, and Oklahoma (then known as Indian Territory). They were first moved onto a southeastern Kansas reservation in the Cherokee Strip, on which the city of Independence, Kansas developed. In 1872 they were forced to move again, south to Indian Territory.

The Upper Louisiana Territory, including the Jasper County area, was renamed as the Missouri Territory on June 4, 1812, to avoid confusion with the state of Louisiana. This had joined the Union in 1812. The new New Madrid District became New Madrid County, Missouri Territory. Old Lawrence County was established in 1815 from New Madrid County west of the St. Francis River and north of Arkansas County. It originally consisted of all of present-day southwestern Missouri and part of northwestern Arkansas.