35,804 born in Greece - Illinois, Northern District Naturalization Index, 1840-1950
FamilySearch.org has a FREE database titled ILLINOIS, NORTHERN DISTRICT NATURALIZATION INDEX, 1840-1950.
35,804 people have Greece listed as their country of birth. You will be able to view the actual index card which contains all the information you need to be able to order your ancestor's naturalization files.
RECORD DESCRIPTION from FamilySearch.org