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The Back Forty
Article #317 December 2020
By Bill Cook

What is a “forty”?  It’s forty acres.  Why forty acres?  Where did this come from?  Why not fifty or a hundred?

     Owning a “forty” has been part of our common vernacular for as long as anyone can remember.  The origins of this measurement harken back to Jeffersonian times.  The young nation was rapidly expanding west.  The usual “metes and bounds” ownership description system, inherited from Europe, was not going to work well. 
     Metes and bounds property boundaries were based on what was seen on the ground, seldom resulting in regular polygons, and sometimes came with odd descriptions.  One such description was ". . . after turning around in another direction, and by a sloping straight line to a certain heap of stone which is by pacing, just 18 rods and about one half a rod more from the stump of the big hemlock tree where Philo Blake killed the bear; . . ." 
     Long story short, after several iterations, authorities agreed upon a survey grid consisting of nested squares.  Each of the “squares” would have a unique description, which would greatly facilitate the transfer of new territory into ownerships.  Deeds and titles needed to be recorded at the nearest Government Land Office before logging, farming, and other land uses could be legally pursued. 
     The grid starting point is called an “initial point”, determined by stellar observations.  Each state would have its own initial point.  From that point, lines would be drawn, north and south.  These lines are called “prime meridians” (north-south) and “baselines” (east-west).  From these primary lines, the land survey grid was built.
     Michigan’s initial point lies south of Mason, near the southern jog in the Ingham County line.  Why the jog?  Well, that’s a story, for another time, that leads to an odd digression in Michigan’s survey history. 
     From the initial point, using the best tools of the day, crews would progress along these basic lines at 24-mile intervals.  These tracts were subdivided into 16 townships.  Each township was divided into 36 square miles.  Each square mile consists of 640 acres and 16 “forties”. 
     “Chains” were the standard linear measure of the day, which are 66-feet long, or 100 “links”.  One mile consists of 80 chains.  A forty is 20 chains by 20 chains.  One acre is 10 square chains.  These measurement units date back, in part, to Roman times based on how much land could be plowed in one day, according some sources. 
     So, all this survey work, done in the 1800s, led to the ownership grid that we use today.  Yes, it’s a bit obscure, but it’s what we have and it’s embedded in our legal system.     
     So, what’s a “forty”?  Well, it’s one of those forty-acre squares.  Each forty, across the nation, has a unique identifier.  This identifier includes state, township, range, section, and subsection(s).  An example for Michigan would be T46N, R25W, Section 3, NWSE.  It describes a township that lies 46 townships north of the initial point, and then 25 townships west.  Within that particular township (Sands Township), the forty is in section 3 (of 36 sections, each 640 acres in size), and sits in the northwest quarter (40 acres) of the southeast quarter (160 acres).  This is a specific forty acre parcel in Marquette County. 
     Not many forties are exactly forty acres.  Think about trying to paste a square of paper on a basketball.  It doesn’t work well.  The rectangular grid system accommodates the curvature of the Earth, with “adjusted”’ rectangles on the north and west sides of a township.  Survey work has the devil in the details, which is one reason why surveyors are licensed.  Nevertheless, surveys are sometimes challenged and sometimes end up in court. 
     More detailed and re-monumented surveys happen every day.  The progression of forest ownership has led to increasingly smaller sizes, a process called parcelization.  In Michigan, less than two percent of the human population owns twenty acres or more.  Collectively, family ownerships amount to over eight million acres, of the twenty million acres of forestland. 
     So, if you own a forested forty, you’re among the few.  And now, perhaps, you can better understand where that “forty” came from.  Manage it wisely. 

More land survey information on the Michigan Forests Forever website.
https://mff.forest.mtu.edu/TreeBasics/Survey.htm

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Survey markers come in different shapes and references.

TRAILER- This website was created by a consortium of forestry groups to help streamline information about forestry and coordinate forestry activities designed to benefit the family forest owner and various publics that make up our Michigan citizenry.  This website is maintained by Bill Cook, Retired Michigan State Extension Forester/Biologist.  Direct comments to cookwi@msu.edu or 906-786-1575.