Illinois (Ill-i-noy'), seventeenth in area of the United States, but third in population, extends from Wisconsin and Lake Michigan on the N. and NE. to the junction of the Ohio and Mississippi rivers at the extreme SW. - a distance of nearly 400 miles. It is bounded E. by Indiana, from which it is partly separated by the Wabash River; S. it is separated from Kentucky by the Ohio; and on the W. the Mississippi flows between it and Iowa and Missouri. The area is 56,650 sq. m., or nearly that of England and Wales. The surface of Illinois is the most level of any state, except Delaware and Louisiana; and its wide grassy plains, though broken by numerous streams fringed with belts of fine timber, have gained for it the name of the Prairie State. The Illinois River is formed by the union of two streams, 45 miles SW. of Lake Michigan, and flows 500 miles SW. to the Mississippi. The fertile soil - a heavy black loam - with a favourable climate, makes this the richest agricultural state in the Union; and Illinois ranks first for the production of corn, cattle, hogs, and horses. The mineral output, especially of bituminous coal, is also large, nearly a fifth of the entire coalfield of the United States being found in this state. Other minerals are lead, limestone, salt, and fluor-spar. The position of Illinois presents unusual facilities for commerce. The rivers that cross or touch the state are navigable for over 400 miles, while by way of the great lakes Chicago has also a water-highway to the Atlantic. Moreover, Illinois has more railroads than any other state, upwards of 10,800 miles. Formerly a part of the North-west Territory, Illinois was organised as a territory in 1809, and admitted as a state in 1818, with a pop. of 34,620. Pop. (1830) 157,445; (1850) 851,470; (1870) 2,539,891; (1880) 3,077,871; (1900) 4,821,550. Chicago is by far the largest city; its limits embrace more than a fourth of the entire population of the state. Peoria, Quincy, Springfield (the capital), and Rockford rank next in population. During the civil war the state contributed 259,092 men to the Union armies, of whom over 29,000 were killed in action or died of wounds or disease. See works by S. Breese (Chicago, 1884), and J. Moses (Chicago, 1889).