The 1940 census included a question on the last full grade that the person had completed in the regular school system-public, private, or parochial school, college, or university. The tabulation of last grade or year of school completed for census tracts is restricted to persons 25 years old and over, practically all of whom have completed their formal education. In the computation of median years of school completed, the first year of high school is uniformly represented by 9, although there are some areas with only 7 years of elementary school.

Three major race classifications are distinguished in this bulletin, namely, white, Negro, and other races. Persons of Mexican birth or ancestry who were not definitely Indian or of other nonwhite race were returned as white in 1940. In tables 3a and 6a statistics for the nonwhite (Negroes and other nonwhite races combined) are shown separately for tracts with 250 or more nonwhite persons. Occupation statistics for nonwhites are presented for Southern cities only. The white population is divided into two nativity groups, native and foreign born. A person born in the United States or in any of its territories or possessions is counted as native. The foreign-born white are presented by country of birth. The country of birth classification is based on political boundaries as of January 1, 1937, and therefore includes such countries as Austria; Czechoslovakia, and Poland.
The age classification is based on the age of the person at his last birthday before the date of the census, that is, the age of the person in completed years.