"United States Census, 1940," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/KW4F-1M4 : accessed 10 Oct 2013), Simon Piersma, Worth Township, Cook, Illinois, United States; citing enumeration district (ED) 16-507B, sheet 16B, family 347, NARA digital publication of T627, roll 790.