Parents and grandparents, the grandparents seem to match those in the census.
Source: "Iowa, Old Age Tax Assistance Records, 1934-1958," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:QLBL-336X
: 7 November 2019), Joseph Leroy Kroll, ; citing Pension, Iowa, United States, multiple county Recorders, Auditors, and County Clerk Offices, Iowa; FHL microfilm 007897314.
Iowa, Old Age Tax Assistance Records
: Pension Iowa, United States
: Joseph Leroy Kroll
: Birth date 12 Feb 1908 Iowa
: Father Thomas Kroll
: Mother Anna Jones
Source: "United States Social Security Death Index," database, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:JLGC-J27
: 15 July 2020), Joseph Kroll, Nov 1969; citing U.S. Social Security Administration, Death Master File, database (Alexandria, Virginia: National Technical Information Service, ongoing).
United States Social Security Death Index
: Joseph Kroll
: Death Nov 1969
: Age 61 Birth 12 Feb 1908
Source: "Wisconsin Marriages, 1836-1930", database, FamilySearch (https://familysearch.org/ark:/61903/1:1:XRGT-TR2
: 30 January 2020), Thomas Kroll, 1906.
Wisconsin Marriages, 1836-1930
: Thomas Kroll
: White Male Birth Wisc
: Father Thomas Kroll Mother Clara Jones
: Marriage 25 Jul 1906 Sparta, Monroe, Wisconsin
: Spouse Anne E. Jones
: White Female Birth Indiana
: Father Uriah Jones Mother Elizabeth Jacques