This report describes the methodology used to develop intercensal estimates of the population of U.S. counties by age, sex, and race for each year from 1970 to 1979 (July 1). An extrapolation to July 1, 1980, is included, along with the census data for April 1, 1970, and April 1, 1980. In addition, the limitations of the estimates are discussed, and comparisons with special censuses are presented.

The estimates are for 5-year age groups to age 85 and over for the total, White, and Black populations by sex. The race classifications for the 1970 and 1980 census data were modified to be consistent with each other and with vital statistics, and the intercensal estimates are consistent by race and age with both the 1970 and 1980 censuses as modified. The age and sex detail in the 1980 census has not been changed, but nearly 6 million persons of Spanish origin were moved out of the category “Other” (race not specified), the vast majority being transferred to White. A similar but much smaller modification was made in 1970. The Black population was not affected by the 1970 procedures and was increased only slightly in 1980. A more detailed description of the modification procedures is given further on.