M. Clay Church (1877-1966) was a businessman from Grand Rapids, Michigan. He worked for his father's company, the Couple Gear Co., which produced the worlds first truck trailers and designed a truck with a motor for each wheel. Church lived in Massachusetts from the late 1920s through the early 1960s, operating the Church Motor Company. Later, he worked as an insurance executive.

A majority of his diary entries relate to his business dealings: what happened at the factory, who he had meetings with, different ideas he was thinking through and records of business transactions. Other entries describe family events and evenings with friends, descriptions of sunrises and various written musings. Also included are lists of addresses, prices of purchasable goods and a stock certificate.