Leavenworth serves as the county seat and largest city within Leavenworth County in the state of Kansas, United States. Situated on the west bank of the Missouri River in northeastern Kansas, it occupies a strategic position at the junction of U.S. Route 73 and Kansas Highway 92. The city lies within the Dissected Till Plains region of North America's Central Lowlands and is part of the broader Kansas City metropolitan area. Its geographic setting is defined by four small tributaries flowing east through the urban landscape: Quarry Creek, Corral Creek, Three Mile Creek, and Five Mile Creek.

Founded in 1854, Leavenworth holds the distinction of being the first city incorporated in the territory of Kansas. It developed south of Fort Leavenworth, which was established as Cantonment Leavenworth in 1827 by Colonel Henry Leavenworth. The city became a key supply base for the settlement of the American West and played a significant role during the Civil War, with many volunteers joining the Union Army. In 1858, the radical Leavenworth Constitution was adopted here, recognizing freed black people as citizens, although it was never approved by the federal government.

The city is notable for its historical association with several prisons, including the United States Disciplinary Barracks and the United States Penitentiary. Fort Leavenworth, which occupied territory outside the city limits until its annexation on April 12, 1977, now occupies the northern half of the city's area. The urban landscape also features an underground series of vaults found in 2008, believed to have been built during the late 19th century. These structures and military installations define much of the city's physical and historical character.

Leavenworth has a complex heritage regarding civil rights and racial history. It attracted refugee African-American slaves seeking freedom from Missouri and became a hotbed of anti-slavery and pro-slavery agitation before the Civil War. The murder of Fred Alexander in 1901 led to the creation of the first state chapter of the Afro-American Council. Benjamin Day became the city's first African-American mayor in 1972, marking a significant milestone in its political history. These events contribute to the city's deep cultural narrative.

As of the 2020 census, the population of Leavenworth was 37,351, making it the 10th most populated city in the Kansas City metropolitan area. The city experiences a humid continental climate with hot, humid summers and cold, drier winters, where January is typically the coldest month and July the hottest. Located 25 miles northwest of downtown Kansas City, it offers access to regional amenities while maintaining its own distinct identity within the state.