Cairo, a city and the county-seat of Alexander county, Illinois, U.S.A., in the S. part of the state, at the confluence of the Ohio and Mississippi rivers, 365 m. S. of Chicago. Pop. (1890) 10,324; (1900) 12,566, of whom 5000 were negroes; (1910 census) 14,548. Cairo is served by the Illinois Central, the Mobile & Ohio, the Cleveland, Cincinnati, Chicago & St Louis, the St Louis, Iron Mountain & Southern, and the St Louis South-Western railways, and by river steamboat lines. The city, said to be the "Eden" of Charles Dickens's Martin Chuzzlewit, is built on a tongue of land between the rivers, and has suffered many times from inundations, notably in 1858. It is now protected by great levees. A fine railway bridge (1888) spans the Ohio. The city has a large government building, a U.S. marine hospital (1884), and the A.B. Safford memorial library (1882), and is the seat of St Joseph's Loretto Academy (Roman Catholic, 1864). In one of the squares there is a bronze statue, "The Hewer," by G.G. Barnard. In the N. part of the city is St Mary's park (30 acres). At Mound City (pop. in 1910, 2837), 5 m. N. of Cairo, there is a national cemetery.
Lumber and flour are Cairo's principal manufactured products, and the city is an important hardwood and cotton-wood market; the Singer Manufacturing Co. has veneer mills here, and there are large box factories. In 1905 the value of the city's factory products was $4,381,465, an increase of 40.6% since 1900. Cairo is a shipping-point for the surrounding agricultural country. The city owes its origin to a series of commercial experiments. In 1818 a charter was secured from the legislature of the territory of Illinois incorporating the city and bank of Cairo. The charter was soon forfeited, and the land secured by it reverted to the government. In 1835 a new charter was granted to a second company, and in 1837 the Cairo City & Canal Co. was formed. By 1842, however, the place was practically abandoned. A successful settlement was made in 1851-1854 under the auspices of the New York Trust Co.; the Illinois Central railway was opened in 1856; and Cairo was chartered as a city in 1857. During the Civil War Cairo was an important strategic point, and was a military centre and depot of supplies of considerable importance for the Federal armies in the west.
In 1862 Admiral Andrew H. Foote established at Mound City a naval depot, which was the basis of his operations on the Mississippi.