When Sylvester Caspar Fellenz was born on 5 March 1911, in Kewaskum, Washington, Wisconsin, United States, his father, Hubert Bernard Fellenz, was 30 and his mother, Margaret Maria Berres, was 29. He married Gertrude Geidel on 13 October 1934, in Saint Michaels, Washington, Wisconsin, United States. He lived in Wisconsin, United States in 1974. He died on 6 February 1974, in West Bend, Washington, Wisconsin, United States, at the age of 62, and was buried in West Bend, Washington, Wisconsin, United States.