Actual state boundaries.—After state boundaries have been described they must be surveyed and marked. Where the boundary line follows a parallel or a meridian the survey may not be so exact as to follow the proposed line with absolute accuracy. The Illinois-Wisconsin boundary line is legally 30' N. lat. The survey of this line varies somewhat from the true parallel. The state line at the shore of Lake Michigan is about one-half mile south, and at the Mississippi River about one-half mile north, of the parallel.
Where the middle of a river forms the boundary line between two states, the center of the main current continues to be the boundary if the channel shifts imperceptibly; hut if the river suddenly changes its course or deserts its original channel the boundary remains in the middle of the deserted channel. This is strikingly illustrated in Randolph County at the junction of the Mississippi and Kaskaskia rivers.
In April, 1SSI, the Mississippi River broke across the narrow peninsula between the Mississippi and Kaskaskia rivers and established a new channel. The site of Old Kaskaskia was destroyed, and Kaskaskia Island was established between the new main channel and the old deserted channel, as shown en the map on page 2. It thus happens that about twenty-five square miles of Randolph County, Illinois, lie on the west side of the Mississippi River and the Mississippi flows across Illinois for a distance of eight miles. The inhabitants of Illinois living on Kaskaskia Island are served by rural mail delivery from St. Marys, Missouri.
Smaller cut-offs have been formed by the Wabash River along the border of White County, Illinois, whereby the main channel of the Wabash crosses Indiana for short distances and small areas of Indiana now lie west of the Wabash River.
Latitude and longitude.—The southernmost point of Illinois is at the junction of the _Mississippi and Ohio rivers in 36° 59' N. lat. The northern boundary of the state is in 42° 30' N. lat. The north-south extent of the state is therefore 51 degrees of latitude, or 385 miles.
The parallel of 40° N. lat. crosses the widest portion of the state and divides Illinois into two approximately equal areas. This central parallel passes just north of Quincy, about twelve miles north of Springfield, ten miles north of Decatur, and ten miles south of Champaign, Urbana, and Danville. Other, but
smaller, cities lying near the same parallel are: Mount Sterling, Beardstown, Petersburg, Lincoln, Clinton, Monticello, and Georgetown. The fortieth parallel crosses ten counties: Adams, Brown, Schuyler, Cass, Menard, Logan, Macon, Piatt, Champaign, and Vermilion.
latitude of Illinois is favorable to the development of a strong, vigorous, and progressive people. its location, some what south of the middle line of the north temperate zone, insures a moderate climate in which farm crops and domestic animals thrive. Its climatic changes are sufficient to stimulate healthful human activity and to encourage productiveness in the various occupations.
The Illinois-Indiana boundary line is in S7° 31' W. long., but the easternmost boundary of the state lies in the middle of Lake Michigan in approximately 87° 5' W. long. The west ernmost bend of the Mississippi along Illinois is in 91° 31' W. long., in Adams and Hancock counties. The extreme width of the state from Indiana to the Mississippi River is 4 degrees of longitude, or 216 miles.
The meridian of 89° west longitude crosses the state almost centrally. The Third Principal Meridian, from which most of the state is surveyed, lies about eight miles west of the eighty ninth meridian. The automobile route known as the Meridian Road extends across the state from north to south and closely parallels the eighty-ninth meridian and the Third Principal Meridian, from Beloit, Wisconsin, and Rockford, Illinois, on the north, to Cairo, Illinois, on the south.
The eighty-ninth meridian passes through or within ten miles of Rockford, La Salle, Peru, Ottawa, Streator, Blooming ton, Decatur, Centralia, and Cairo. Other, but smaller, cities lying near the same meridian are: Belvidere, Rochelle, Men dota, Springvalley, Minonk, Normal, Clinton, Vandalia, Salem, Mount Vernon, Benton, Herrin, Carterville, Johnston City, Marion, Vienna, and Mound City. The eighty-ninth meridian crosses sixteen counties: Winnebago, Ogle, Lee, La Salle, Woodford, McLean, Dewitt, Macon, Shelby, Fayette, Marion, Jefferson, Franklin, Williamson, Johnson, and Pulaski.