The Prairie Mills Windmill is one of four remaining smock windmills in Illinois and one of only seven smock windmills remaining in the midwest.  It is one of three windmills that still has its original stones and operating mechanism.  It is similar in design to windmills seen in the Netherlands. 

A nearly identical "sister" windmill still stands in Felde, Germany.  Felde is located the Ostfriesland/Hanover region in Northwestern Germany between Wilhemshaven and the Netherlands border.  Mr. Henrich Reemts Emminga built the Golden and Felde windmills.

A windmill uses simple but effective concepts to perform its job (see illustration).  In a smock mill, sails are designed similar to airplane propellers to catch the wind and spin.  The sails drive the horizontal "wind shaft" and the "brake wheel" located in the top of the mill.  The brake wheel spins another wheel called the "wallower" located at the top of the vertical "main spindle."  The "great spur wheel" at the bottom of the main spindle engages a "stone nut" which turns the millstones through the "stone spindle."

The Prairie Mills Windmill has four levels or "floors".  The "meal floor" is at ground level and is where the ground flour is collected and sacked.  The "stone floor" is where the millstones are located.  The "sack hoist floor" houses most of the operating mechanism and is where grain is loaded into holding bins.  The "cap floor" houses the wind shaft (what the "sails" are connected to), the brake wheel, the wallower, and the mill brake.

Windmills use gravity to feed grain through the millstone and to catch the flour.  This requires grain to be lifted from the "meal floor" to the "sack hoist floor."  Instead of carrying individual bags of grain up two flights of stair, millers use the "sack hoist" to raise the grain.  The sack hoist is a simple horizontal shaft and a rope that is tied to a grain sack.  As the shaft rotates, the sack rope winds around the shaft and lifts the sack.

The Prairie Mills Windmill has three sets of millstones.  Each set consists of a bed stone (on the bottom) and a runner stone (on the top).  The bed stone is fixed on the meal floor and the runner stone rotates above it.  The spacing between the runner stone and bed stone largely determines the quality of the flour.  Different millstones were probably used to grind specific types of grain..  For example, one set may be used for milling buckwheat, a soft grain with a high oil content.  Others would be used to mill harder wheat, rye, oats or corn.  However, the windmill could only turn one set of millstones.

The "cap floor" is the top of the windmill.  It houses the brake wheel, brake, and wind shaft on which the sails are attached.  The "cap" can rotate in any direction. 

Millers use a "winder" system to turn the cap and the sails into the wind.  A miller uses the "capstan wheel" and a "winding chain" to wind the sails.  The "stage" on the outside of the mill tower provides anchor points for the chain.  Although the total weight of the cap, sails, and mechanism exceeds 20 tons (40,000 pounds), one miller can normally turn the cap.

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