I can't find Robert or his daughters Nettie and Minnie in any Census prior to 1930.
1930 Henry, Okmulgee, OK
Robert P. Moore, b. TX 45, marr abt. 5 yrs, general farmer
Lula M., wife, b. OK, 25
Nettie, b. OK, 18
Minnie, b. OK, 11
Mamie, b. OK, 4
Robert P., b. OK, 3
Myrtle, b. OK, 1
Robert P. Moore, b. TX, 56, farmer
Myrtle Lulu, wife, b. OK, 35
Edith, b. OK, 13
Robert, b. OK, 12
Myrtle, b. OK, 11
Pauline, b. OK, 9
Clarence, b. OK, 8
Lloyd, b. OK, 7
Charley, b. OK, 5
Betty Lou, b. OK, 3
Ruby, b. OK, 2
Lilly, b. OK, 0
Robert P "Poppy" Moore
Born: Dec 26 1884
Died: March 16, 1966
Buried: Salem Cemetery, Dewar, Okmulgee, OK
Source: findagrave.com with more info & pic of tombstone
This doesn't tell you where he died. Oklahoma doesn't publish a death index which makes it difficult to find or verify where a person dies.
I looked for his obituary online but didn't find it. One option is to contact the Okmulgee County Genealogical Society, www.okmulgeecountygenealogicalsociety.org/.
Another option is to contact Oklahoma State Dept health, www.ok.gov/health/Birth_and_Death_Certificates/Death_Certif... and use the death date above and that he died in Okmulgee Co. IF the Informant at the time of his death knew, his parents might be on his death certificate.
I also found the Hill Family Tree, ancestry.com which contains Robert and they show his parents as Finley Moore, b. March 23, 1860, Washington Co., NC.
The Farrimond Family Tree, ancestry.com contains Robert Port "Jack" Moore (I searched the Census records for Jack too) b. Dec 26, 1884, Farmersville, Collin, TX and died March 16, 1966, Henryette, Okmulgee, OK.
Most larger libraries provide free access to ancestry.com. The Farrimond family tree also has a picture of Jack and his wife (I'm sure he had more than one).