Paducah (/pəˈduːkə/ ^ⓘ pə-DOO-kə) is a home rule-class city in the Upland South, and the county seat of McCracken County, Kentucky, United States. The most populous city in the Jackson Purchase region, it is located in the Southeastern United States at the confluence of the Tennessee and the Ohio rivers, halfway between St. Louis, Missouri, to the northwest and Nashville, Tennessee, to the southeast. As of the 2020 census, the population was 27,137, up from 25,024 in 2010. Twenty blocks of the city's downtown have been designated as a historic district and listed on the National Register of Historic Places.

Paducah is the principal city of the Paducah metropolitan area, which includes McCracken, Ballard, Carlisle and Livingston counties in Kentucky and Massac County in Illinois. The total population of the metro area was 103,481 in 2020. The Paducah–Mayfield combined statistical area had a total population of 140,138.

Paducah was first settled as "Pekin" around 1821 by European Americans James and William Pore. The town was laid out by explorer and surveyor William Clark in 1827 and renamed Paducah.

Although local lore long connected this name to an eponymous Chickasaw chief "Paduke" and his band of "Paducahs", authorities on the Chickasaw have since said that there was never any chief or tribe of that name, or anything like it. The Chickasaw language does not have related words. Instead, historians believe that Clark named the town for the Comanche people of the western plains. They were known by regional settlers as the Padoucas, from a Spanish transliteration of the Kaw word Pádoka or the Omaha Pádoⁿka.

Paducah was formally established as a town in 1830 and incorporated as a city by the state legislature in 1838. The city charter was drafted by Quintus Quincy Quigley and H. Clay King in 1856.

By this time, steam boats traversed the river system, and its port facilities were important to trade and transportation. In addition, developing railroads began to enter the region. A factory for making red bricks, and a foundry for making rail and locomotive components became the nucleus of a thriving "River and Rail" economy. Paducah became the site of dry dock facilities for steamboats and towboats, and thus headquarters for many barge companies. Because of its proximity to coalfields further to the east in Kentucky and north in Illinois, Paducah also became an important railway hub for the Illinois Central Railroad. This was the primary north–south railway connecting the industrial cities of Chicago and East St. Louis to the Gulf of Mexico at Gulfport, Mississippi, and New Orleans, Louisiana. The Illinois Central system also provided east–west links to the Burlington Northern and the Atchison, Topeka, and Santa Fe Railways (which later merged to become the BNSF Railway).

In 1924 the Illinois Central Railroad began construction at Paducah of their largest locomotive workshop in the nation. Over a period of 190 days, a large ravine between Washington and Jones streets was filled with 44,560 carloads of dirt to enlarge the site, sufficient for the construction of 23 buildings. The eleven million dollar project was completed in 1927 as the fourth-largest industrial plant in Kentucky. The railroad became the largest employer in Paducah, having 1,075 employees in 1938.

As steam locomotives were replaced through the 1940s and 1950s, the Paducah shops were converted to maintain diesel locomotives. A nationally known rebuilding program for aging diesel locomotives from Illinois Central and other railroads began in 1967. The shops became part of the Paducah and Louisville Railway in 1986. In the early 21st century, they are operated by VMV Paducahbilt.