Cook County Plat (1832)

The General Land Office (GLO) surveyed Cook Country in 1832, 1834, and 1842. This unsigned manuscript plat, dated 1832, shows the area surrounding the mouth of the Chicago River. Other plats from the same survey chart the lands immediately to the north and south. The handwritten annotation in the lower left mentions that the land mapped was included in the “canal lands,” meaning that it was part of the 284,000 acres assigned to the canal commissioners in 1822 by the federal charter grant of land.  The commissioners then raised the money to construct the canal by selling off parcels of the land. (For more on the canal lands and their acquisition from Native Americans, see The Chicago Portage).

The drawing details the area’s chief natural and manmade features, indicating the contour of the shoreline and the extent of forests, pastures, and marshes. Following cartographic convention, the map indicates the rivers and lakeshore in blue watercolor, and the timberline in green.  The manuscript also marks the location of Fort Dearborn, which had been erected by the U. S. Army in 1803 and rebuilt following the War of 1812.

The GLO drawing illustrates how the city’s initial platting largely determined its gridded structure. The north-south lines on the plat trace what would become State Street (closest to the lake), Halsted Street, Ashland Avenue, and Western Avenue (marking the western edge of the plat).  The “true line” extending westward from the lake would become North Avenue and mark the northern boundary of the town. The original demarcation between the town of Chicago and the rest of the canal lands would become Division Street. The east-west lines below mark the eventual locations of Chicago Avenue, Madison Street, Twelfth Street (Roosevelt Road), and 39th Street (Pershing Road.)

The sheet also records the surveyor’s technical notes.  The diagonal lines in the lower left indicate the earth’s magnetic variation, showing the difference between magnetic north and true north.  The text within the area of the lake explains the methods by which the plat was made.

See also: The National Grid



Danzer, Gerald. “Chicago’s First Maps.” In Chicago Mapmakers: Essays on the Rise of the City’s Map Trade, edited by Michael P. Conzen. Chicago: Chicago Historical Society for Chicago Map Society, 1984.

Holland, Robert. Chicago in Maps: 1612-2002. New York: Rizzoli, 2005.

Johnson, Hildegard Binder. Order upon the Land: The U.S. Rectangular Land Survey and the Upper Mississippi Country. New York: Oxford University Press, 1976.

“Cook County Plat, T39, R14E,” in US Surveyor General’s Records for Illinois, “Federal Township Plats,” Illinois State Archives, Record Series 953.012, 1832