R2 Systems, San Diego
December 12, 1999
The basic unit of the Township and Range System is the section, which is nominally a square one mile on each side (i.e., a square mile, which is 640 acres). Sections are combined into townships, which are nominally squares that are six miles on a side. Therefore, each township contains 36 sections (square miles). I've used the word nominally in these descriptions because individual townships and sections sometimes vary from these definitions (in some case, by quite a bit). These surveys were conducted in the early 19th century, and geographical, technological and political considerations caused the survey teams to sometimes make mistakes or take liberties with the strict definitions.
Townships are named by their distance from a base line and a principal meridian. These are arbitrary lines that run east-west (base lines) and north-south (principal meridians). For Missouri, the base line is located about the middle of Arkansas, with the result that all Missouri townships are "Township <number> North" (e.g., "Township 43 North"). The principal meridian for Missouri is the "5th Principal Meridian", which runs just east of Jefferson County; thus, all townships in the county are "Range <number> East" (e.g., "Range 6 East").
Within a section, land descriptions often divide it into "halves" and "quarters". You will see descriptions like "The East half of the Northwest quarter of Section Twentythree in Township Forty North of Range Three East", which is the description of the 80-acre tract that we believe is the first land owned in Missouri by our great-greatgrandfather. On the map at this link, this tract is southeast of the center of the image; the north-south portion of Russell Road should run just about through the middle of it.
A much more complete (and clearer) discussion of this, with very good pictures, is at Infobahn Outfitters.