OK - so I looked up North Dakota Charles O's - and found this:
"United States Census, 1920," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:MC8G-JRR : 14 December 2015), Charles E Miller in household of Homer C Miller, Zion, Towner, North Dakota, United States; citing sheet 10A, NARA microfilm publication T625 (Washington D.C.: National Archives and Records Administration, n.d.); FHL microfilm 1,821,340.
"United States Census, 1930", database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:X41F-SP3 : 8 December 2015), Charles O Miller Jr. in entry for Charles O Miller, 1930.
"United States Census, 1940," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:VR2X-1M2 : accessed 12 August 2016), Charles Miller in household of C N Miller, Byron Township, Stafford, Kansas, United States; citing enumeration district (ED) 93-2, sheet 2A, family 25, Sixteenth Census of the United States, 1940, NARA digital publication T627. Records of the Bureau of the Census, 1790 - 2007, RG 29. Washington, D.C.: National Archives and Records Administration, 2012, roll 1262.
Looks like they moved around a lot. Father from Indiana, he was born in North Dakota, moved to Indiana, then to Kansas - I suppose they could have ended up in Texas, or he enlisted and after the war ended up in Texas. I'm OK with that story too.