Cyrus Hall McCormick improved and patented the mechanical reaper, which eventually led to the creation of the combine harvester.

Each of these buildings played a specific role in the daily routine of the Cyrus McCormick farm.

The McCormick Farm at Walnut Grove is known as the birthplace of the mechanical reaper, the predecessor to the combine harvester.

Cyrus McCormick reportedly designed, built, and tested his reaper all within six weeks at Walnut Grove, although the design may have been an improvement upon the similar device developed by his father and his brother Leander over a period of 20 years.

After building his first reaper, Cyrus repeatedly went back to the drawing board to revise and improve his basic design.

After his father's death, Cyrus McCormick moved his base of operations from Rockbridge County, Virginia to Chicago, Illinois in 1847 because of the vast acreage of fertile prairie soil in the midwestern United States.

By the end of the 19th century, McCormick's company had built a primitive combine, which could harvest grain even faster and cheaper than older reapers.