For most of the United States, "Census Day" for the 1980 enumeration was April 1, 1980. As in past censuses, all questionnaires were to be completed giving information as of that date, regardless of when the form was actually completed.
The use of a mailout/mailback questionnaires in 1970 had proven successful and eased the follow-up operation burden. Furthermore, tests during the 1970 census indicated the feasibility of administering a mailout/mailback census in rural areas and small towns. As a result, the census areas receiving questionnaire by mail in 1980 covered 95.5 percent of the United States population.