John Mousley Cannon was a successful lawyer in Salt Lake City from the late 1800's until his death in 1917. He had several financial ventures in mining, real estate, and livestock, and many of the papers in the collection describe these investments. The John M. Cannon papers also contain personal correspondence between Cannon and one of his father's six wives, Johanna C. Danielson Cannon, whom John calls "Aunt Johanna." John Cannon himself had two wives, and possibly a third, although they are not mentioned in the papers.

Legal documents in the collection describe Cannon's law practice in Salt Lake City and contain information about politics, leases, and monetary disputes between Utahns in the late nineteenth and early twentieth centuries.

Two letters from LDS missionaries are included, one being his nephew, Vaughn, who served in Germany in 1914, and the other a friend, Alfred Jensen, who served in Missouri in 1901.