U.S. Census Office, The Progress of the Nation 1790-1820 (1874)

These maps were featured in the U.S. Census Office's Statistical Atlas of the United States Based on the Results of the Ninth Census, 1870. This Statistical Atlas, the first of several, was published in 1874 under the supervision of Superintendent Francis Walker, who wanted to mark the upcoming centennial of the United States by illustrating its progress over the last century, including the expansion of settlement. His statisticians did so by plotting the westward encroachment of population density data from each census on a series of maps over eight decades. These four maps depict the first four decades: 1790, 1800, 1810, and 1820. They can be compared with data maps from 1830-1840, 1850, and 1860, also featured on this site. The grayscale on the maps uses darker colors to indicate higher population densities, with the darkest shade indicating 90 or more inhabitants per square mile and the lightest gray indicating 2 to 5 inhabitants per square mile. The white indicates fewer than 2 inhabitants per square mile. In an accompanying section of the Statistical Atlas titled "The Progress of the Nation: 1790-1870," Walker famously discusses the  population line separating the area of European-American settlement (colored in different shades of gray) and the frontier (shown in white), which would become known as the "frontier line." In that same section (see pp. 1-2), Walker calculated that the total settled area of the United States in 1790 was 239,935 square miles, with a population of 3,929,214 and an average density of 16.4 inhabitants per square mile. By 1800, the settled area expanded to 305,708 square miles, with a population of 5,308,483 and an average density of 17.3 inhabitants per square mile. In 1810, the settled area increased to 407,945 square miles, with a population of 7,239,881 and an average density of 17.7 inhabitants per square mile. By 1820, the settled area reached 508,717 square miles, with a population of 9,633,822 and an average density of 18.9 inhabitants per square mile. It is important to note that the Native American population was not included in this census data. Indeed, of  the 1820 map, Walker writes, "the frontier line now rests, when it has run its course, upon the Gulf of Mexico, instead of returning to the Atlantic ; while this southwest connection has embraced within the frontier one other great vacant tract, soon, however, to be devoured by population. This interior unsettled tract I may call the Central Southern, consisting as it does of the extreme southeast corner of Tennessee, the extreme southwest corner of North Carolina, the eastern half of Alabama, and the western and southern portions (far more than the half) of Georgia, Most of this is occupied by Indians, for whose removal negotiations are already in progress" (p. 2).