Fourth principal meridian

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U.S. Bureau of Land Management map showing the principal meridians of Ohio, Indiana, and Illinois

The fourth principal meridian, set in 1815,[1] is the principal meridian for land surveys in northwestern Illinois and west-central Illinois,[2] and its 1831[3] extension is the principal meridian for land surveys in Wisconsin and northeastern Minnesota.[1][2] It is part of the Public Land Survey System that covers most of the United States.

The fourth principal meridian begins at a point on the west bank of the Illinois River in Schuyler County, Illinois. The fourth principal meridian's baseline, sometimes called the Beardstown baseline,[citation needed] runs west from this initial point.[1][2] The meridian and this baseline governs surveys in Illinois that are west of both the Illinois River and the third principal meridian.[2]

The Illinois Department of Transportation 2003 Survey Manual gives the point as 40°0′50″N 90°27′11″W / 40.01389°N 90.45306°W / 40.01389; -90.45306Coordinates: 40°0′50″N 90°27′11″W / 40.01389°N 90.45306°W / 40.01389; -90.45306 and notes that the meridian is an extension of the line north from the mouth of the Illinois River near Grafton, Illinois.[1]


The meridian was extended north in 1831, through Wisconsin and northeastern Minnesota.[3] The extension uses the Illinois–Wisconsin border as its baseline,[1][2] and is the basis of surveys in all of Wisconsin, as well as that part of Minnesota:

The initial point of the extended fourth principal meridian is located at 42°30′27″N 90°25′37″W / 42.50750°N 90.42694°W / 42.50750; -90.42694.

See also[edit]


  1. ^ a b c d e "Chapter Five: Land Surveying". Survey Manual (PDF). Springfield, Illinois: Illinois Department of Transportation, Bureau of Design and Environment. 2003-02-28. pp. 5–5. Retrieved 2008-10-30. 
  2. ^ a b c d e f Raymond, William Galt (1914). Plane Surveying for Use in the Classroom and Field (via Google Books) (2nd ed.). New York: American Book Company. p. 456. 
  3. ^ a b "Part 5: Public Land Survey System". National Mapping Program Technical Instructions: Standards for USGS and USDA Forest Service Single Edition Quadrangle Maps (PDF) (Draft for Implementation ed.). March 2003. pp. 5A–2–5A–4. Retrieved 2008-10-31. 
  4. ^ Minnesota Geospatial Information Office

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