Pekin is a city in and the county seat of Tazewell County in the U.S. state of Illinois. Located on the Illinois River, Pekin is the largest city of Tazewell County and the second most populous municipality of the Peoria metropolitan area, after Peoria itself. As of the 2020 census, its population is 31,731. A small portion of the city limits extend into Peoria County. It is a suburb of Peoria and is part of the Peoria Metropolitan Statistical Area.

The Illinois River is a principal tributary of the Mississippi River at approximately 273 miles (439 km) in length. Located in the U.S. state of Illinois, the river has a drainage basin of 28,756.6 square miles (74,479 km2). The Illinois River begins with the confluence of the Des Plaines and Kankakee rivers in the Chicago metropolitan area, and it generally flows to the southwest across Illinois, until it empties into the Mississippi near Grafton, Illinois. Its drainage basin extends into southeastern Wisconsin, northwestern Indiana, and a very small area of southwestern Michigan in addition to central Illinois. Along its shores are several river ports, including Peoria, Illinois. Historic and recreation areas on the river include Starved Rock, and the internationally important wetlands of the Emiquon Complex and Dixon Waterfowl Refuge.