The gross area, land and water, of the United States and its outlying areas at the time of the 1960 Census was 3,628,150 square miles (table 1). Puerto Rico and the outlying areas had an area of 12,939 square miles and constituted less than 0.4 percent of the aggregate area.

The area in 1790 was 888,811 square miles, or somewhat less than one-fourth of the present area, and embraced substantially all the territory between Canada and Florida and between the Atlantic Ocean and the Mississippi River, together with part of the drainage basin of the Red River of the North. This original territory and the successive major accessions of territory from 1790 to 1920 are shown in figure 3. In 1803, the area of the country was nearly doubled by the Louisiana Purchase; and, between 1840 and 1850, three large accessions of territory resulted in further increases aggregating 1,204,741 square miles, equivalent to two-thirds of the former area.

Table C. Territory of the United States And Its Outlying Areas: 1790 To 1960
[Gross area (land and water) in thousands of square miles]

Year	Total	States1	Other2
1960	3,628	3,615	13
1950	3,628	3,022	606
1940	3,735	3,022	713
1930	3,735	3,022	713
1920	3,735	3,022	713
1910	3,735	2,787	948
1900	3,735	2,717	1,018
1890	3,600	2,632	977
1880	3,600	2,087	1,521
1870	3,609	1,983	1,626
1860	3,022	1,713	1,309
1850	2,998	1,582	1,461
1840	1,788	935	853
1830	1,788	821	967
1820	1,788	754	1,034
1810	1,716	514	1,202
1800	880	526	363
1790	880	517	372

¹For the most part, the 1960 area of each State was used in computing the area included in the States at each decade. Minor adjustments in State boundaries were ignored, but major changes, such as the decreases in the area of Georgia prior to 1800 and 1810 when parts of the original area of the State were ceded to the Federal Government, are reflected in the figures.
²Includes the Commonwealth of Puerto Rico, the Territories prior to becoming States, and outlying areas of sovereignty or jurisdiction.

Source: U.S. Department of Commerce, Bureau of the Census, Historical Statistics of the United States, Colonial Times to 1957, Washington, D.C., 1960, Series Jl-2, and records of the Bureau of the Census.

For the United States, the population per square mile of land area in 1960 was 50.5 (table 2). For conterminous United States, that is, the United States excluding Hawaii and Alaska, the figure for 1960 was 60.1 as compared with 50.7 for the same area in 1950. Beginning with the Census of 1790, in which the population per square mile was 4.5, the figures at each subsequent, census have shown an increase in density with the exception of those for the Censuses of 1810 and 1850. In each of these years, the density was lower than it had been in the immediately preceding census because of large accessions of sparsely populated territory in the preceding decade.

Land includes dry land and land temporarily or partially covered by water, such as marshland, swamps, and river flood plains; streams, sloughs, estuaries, and canals less than one-eighth of a statute mile in width; and lakes, reservoirs, and ponds having less than 40 acres of area. The presentation of area measurements may be for total or gross area, including land and inland water.

The land area figures of incorporated places generally were supplied by city engineers. The definition of land as employed by the Bureau may not have been observed by those outside the Bureau, but the reasonableness of their measurements were reviewed before inclusion in the publications. Other area figures were supplied by government officials or other well informed sources, or were obtained by planimeter measurements of the best available maps.
Changes in areas from previous dates result from changes in boundaries and from re-measurements based on more accurate information. Transfers between land and water areas occur through construction of dams and reservoirs or the filling in of water area.