1935, Warrensburg, Missouri
1940 Saint Louis, St. Louis, MO
Mack Jackson, TX 57, no occ, education=high school 1 yr
Josephine, wife, b. MO, 50, educ=8th grade
Mildred, dau, b. MO, 29, machine operator envelope firm, educ=8th grade
Born: Dec 4, 1881
First Enlisted: 6 May 1905
Enlisted U. S. Army: 1 Sept 1935
Retired U. S. Army: 30 Sept 1936
Died: 28 Oct 1955
Buried: Nov 2, 1955, U. S. Soldiers & Airmen's Home National Cemetery, Washington D. C.
Mrs. Josephine S. Jackson, wife, St. Louis, MO signed order for his tombstone.
Source: U. S. national Cemetery Interment Control Forms 1928-1962
I imagine he died in St. Louis, MO but don't know for sure. I'd look for a copy of his obituary there too.
If he was career military that explains why he doesn't appear in the Census records until 1940. Successful Searching!