Demography is the statistical study of human populations. It includes the study of the size, structure, and distributions of different populations and changes in them in response to birth, migration, aging, and death. It also includes the analysis of the relationships between economic, social, cultural, and biological process influencing a population. The field of sociology draws on huge bodies of data generated by a variety of sources, including the U.S. Census Bureau.

Demography is widely used for various purposes and can encompass small, targeted populations or mass populations. Governments use demography for political observations, scientists use demography for research purposes, and businesses use demography for the purpose of advertising.

Statistical concepts essential to demography include birth rate, death rate, infant mortality rate, fertility rate, and life expectancy. These concepts can be further broken down into more specific data, such as the ratio of men to women and the life expectancy of each gender. A census helps provide much of this information, in addition to vital statistic records. In some studies, the demography of an area is expanded to include education, income, the structure of the family unit, housing, race or ethnicity, and religion. The information gathered and studied for a demographic overview of a population depends on the party utilizing the information.

From the census and vital statistics gathered using a wide variety of sources, sociologists can create a picture of the U.S. population - who we are, how we are changing, and even who we will be in the future.