"Massachusetts Births, 1841-1915," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:FXJS-6WB : 11 March 2018), John Francis Hellen, 08 Oct 1907, Hudson, Massachusetts; citing reference ID #pg 463 ln 97, Massachusetts Archives, Boston; FHL microfilm 2,315,133.
"United States Census, 1940," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:K7MD-71S : 22 November 2019), John Hellen, Assembly District 12, Manhattan, New York City, New York, New York, United States; citing enumeration district (ED) 31-1055, sheet 10A, line 14, family 279, 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 2649.
"United States, GenealogyBank Obituaries, 1980-2014," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:QV54-HSPX : accessed 13 March 2020), Mary Flaherty Hellen in entry for John F Hellen Jr, Massachusetts, United States, 13 Jan 1990; from "Recent Newspaper Obituaries (1977 - Today)," database, GenealogyBank.com (http://www.genealogybank.com : 2014); citing , born-digital text.
"Massachusetts Death Index, 1970-2003", database, FamilySearch (https://familysearch.org/ark:/61903/1:1:VZ5Y-G55 : 13 June 2019), John F Hellen, 1990.