The Third Principal Meridian

The Third Principal Meridian. . At the point where U.S. Highway 51 and the Jefferson-Marion County road meet, the Third Principal Meridian intersects its east-west base line. This cardinal point was established by a Federal surveyor on February 1, 1815. At least 60 percent of the land in Illinois is measured from and identified by these two important coordinates., In the original thirteen states land had been measured by metes and bounds, employing known landmarks and compass points, but the system had proved inaccurate and impermanent. As a result, the Jefferson Committee on Public Lands devised the rectangular method in 1784. It became law the following year with the passage of the Land Ordinance of 1785, which applied to government lands not yet surveyed in the area northwest of the Ohio River., The ordinance stated that "The surveyors, as they are respectively qualified, shall proceed to divide the said territory into townships of six miles square, by lines running due north and south, and others crossing these at right angles, as near as may be." Each new survey had to be tied to a principal meridian and its base line. The First Principal Meridian was laid out to govern land mostly in the Ohio country; the Second, mostly in Indiana; and the Third--running due north from the confluence of the Ohio and Mississippi rivers--in Illinois only., Surveyors' townships are numbered north and south of a base line and placed in ranges that are numbered east and west of a meridian. Unless a township is fractional, it is further divided into 36 sections, each measuring one mile by one mile. A full section contains 640 acres.