William F. Kohlman, Missouri
I think I may have found William F. Kohlman in Jackson County, Kansas City Missouri, 1920.
Kohlman, William F., 48, Missouri, GER, GER, Baker
Anna, wife, 26, Missouri, Missouri, Missouri
Francis L, 5, Oklahoma
Harry "King" Kohlman lists his father as being born in Missouri, also, Harry's social security number was issued in Oklahoma.
William could have been working on the railroad in Oklahoma before moving to Missouri and Harry could have lived in Oklahoma with him before moving back to Indiana.
I can't find a death record for Francis, so it's possible that he or any children William had after 1920 could still be living.