U.S. Census Office, Native Population 1870. By States and Territories (1874)

This set of population pyramids was featured in the 1874 Statistical Atlas of the United States based on the Results of the Ninth Census 1870, published under the direction of Francis A. Walker. It illustrates demographic patterns related to native and foreign-born populations by state. In each pyramid, the left side represents the male population and the right side represents the female population. The vertical axis displays age groups, with younger ages (beginning with those under ten years of age) at the bottom. While the length of the horizontal bars in most modern population pyramids indicate the percentage of the population, each of these bars represents the part per thousand (the per mille of the population). In other words, if you add up the numbers on each side of a population pyramid in this display it will come out to 1000, instead of 100 like it would in the population pyramids we usually see today. Where one side of a pyramid is shaded, it indicates that there are more people of that gender than the other. The first series of population pyramids focuses on native populations, which Walker defined as individuals born to parents who were themselves born in the United States. While many states display relatively balanced gender distributions, others—including Colorado, Dakota, Idaho, Montana, and Wyoming—exhibit disproportionately large male populations. A similar pattern appears in the second series of pyramids, which represents the foreign-born populations of each state. These demographic patterns reflect the role of westward expansion, as these states lay along the frontier and attracted large numbers of men seeking employment in male-dominated occupations such as surveying, logging, mining, and farming. Immigrants were likewise drawn to these regions by economic opportunity. The foreign-born population pyramids also display pronounced bulges in the middle age groups, indicating a higher proportion of working-age adults. This pattern reflects the tendency of many immigrants to arrive in the United States during their prime working years, often with the intention of settling and forming families.