Lewis Cass McCormick was born March 17, 1856 to William Thomas McCormick and Susan B. Paxton in Rochester, Missouri. On February 27, 1877, Lewis McCormick and Katherine May Martin were married in Shawneetown, Illinois. Katherine was only sixteen years old. Her mother, America Spoors, gave her consent for the marriage.
Lewis and Katherine would have seven children – three boys and four girls:
- Willie McCormick, born November 23, 1877 in Shawnetown, Illinois
- Gertrude McCormick, born July 11, 1879 in Shawnetown, Illinois
- Bessie McCormick, born November 24, 1882 in Alma, Wisconsin
- Orville McCormick, born July 28, 1886 in Excelsior, Minnesota
- Estelle, born January 2, 1890 in Excelsior, Minnesota
- Addison, born June 27, 1892 in Excelsior, Minnesota