The U.S. Census Bureau collects and publishes data on populations in the United States according to several different definitions. Various statistical systems then use the appropriate population for calculating rates. (Also see Sources and Definitions, Population Census and Population Estimates.)
Civilian noninstitutionalized population
Civilian population excluding people residing in institutions (such as nursing homes, prisons, jails, mental hospitals, and juvenile correctional facilities). Census Bureau estimates of the civilian noninstitutionalized population are used to calculate sample weights for the National Health Interview Survey, National Health and Nutrition Examination Survey, and National Survey of Family Growth
Resident population excluding those who are in the active-duty military, although families of members of the armed forces are included. Civilian population includes both institutionalized and noninstitutionalized people.
Includes people whose usual place of residence (that is, the place where one usually lives and sleeps) is in 1 of the 50 states or the District of Columbia. It includes members of the armed forces stationed in the United States and their families. It excludes members of the armed forces stationed outside the United States and civilian U.S. citizens whose usual place of residence is outside the United States. The resident population is the denominator used to calculate birth and death rates and incidence of disease.