The Base Line Survey

One of two Illinois sites that form the basis for all land surveys in the state lies just northwest of Beardstown, where the 4th principal meridian intersects its base line. Land was originally measured by metes and bounds using known landmarks as reference points, with boundary lines set by compass lines or natural features such as streams, but this system proved unsatisfactory because landmarks can change and compass lines can vary. In May 1785, Congress adopted the rectangular system of land measurement, establishing in each state or group of states one or more north-south principal meridians and one or more east-west base lines on parallels of latitude at right angles to one another. Determined by astronomical observation and numbered, the 3rd and 4th principal meridians intersect their respective base lines in Illinois and govern all land measurement in the state. Parallel lines at six-mile intervals east and west from each principal meridian create divisions called ranges, numbered consecutively in each direction, while similar lines parallel to the base line mark divisions called townships. The six-mile squares formed by these intersecting lines are government townships, which are located in relation to a principal meridian by township and range designations such as range 2 west, township 3 north. Government townships are further divided into 36 numbered sections containing 640 acres, and acres form the basis of most property identification.

Illinois · United States