The United States Federal Census began in 1790 and is taken every 10 years. Census returns from 1790 through 1840 list the names of the heads of household only, and count other household members by age range and gender only. The 1850 census was the first year every household member was listed by name, however, relationships of individuals to the head of household were not included until 1880. Individual population schedules for the 1940 census are the most recent available to researchers.
Blank census forms are useful in at least a couple of different ways: (1) they provide an overview of the questions asked on a given population schedule, and (2) they are one way of recording data of interest when researching individuals and families in the census. Several sites provide free downloadable census forms for use by researchers.