Cairo, Illinois

Cairo (/ˈkɛəroʊ/ KAIR-oh, sometimes /ˈkeɪroʊ/ KAY-roh) is the southernmost city in Illinois and the county seat of Alexander County. A river city, Cairo has the lowest elevation of any location in Illinois and is the only Illinois city to be surrounded by levees. It is in the river-crossed area of Southern Illinois known as "Little Egypt", for which the city is named, after Egypt's capital on the Nile. The city is coterminous with Cairo Precinct.

The city is located at the confluence of the Ohio and Mississippi rivers, some of the largest rivers in North America, and is near the Cache River complex, a Wetland of International Importance. Settlement began in earnest in the 1830s and busy river boat traffic expanded through the 1850s. Fort Defiance, a Civil War base, was located here in 1862 by Union General Ulysses S. Grant to control strategic access to the rivers, and launch and supply his successful campaigns south. Developed as a river port, Cairo was later bypassed by transportation changes away from the large expanse of low-lying land, wetland, and water, which surrounds Cairo, and due to industrial restructuring, the population peaked at 15,203 in 1920, while in the 2020 census it was 1,733.

Several blocks in the town comprise the Cairo Historic District, listed on the National Register of Historic Places (NRHP). The Old Customs House is also on the NRHP. The city is part of the Cape Girardeau–Jackson, MO–IL Metropolitan Statistical Area.

The entire city was evacuated during Mississippi River floods in 2011, after the Ohio River rose higher than the 1937 flood levels, with the possibility of 15 feet of water inundating Cairo. The United States Army Corps of Engineers breached levees in the Mississippi flood zone near Cairo in Missouri to prevent flooding in Cairo and other more populous areas further downstream along both the Ohio and Mississippi rivers.