The population of the United States on April 1, 1960, was 179,323,175; this figure represents an increase of nearly 28 million, or 18.5 percent, over the corresponding figure for April 1, 1950 (table 2). In absolute numbers this increase is greater than the increase during any previous intercensal period. In relative terms, the increase between 1950 and 1960 was the largest increase since the decade 1900 to 1910. It falls considerably short, however, of any of the decennial rates of increase which occurred during the nineteenth century.

The population of conterminous United States, that is, the United States excluding the newly admitted States of Alaska and Hawaii, was 178,464,236 on April 1, 1960. This figure represents an increase of about 27.8 million, or 18.4 percent, over the corresponding 1950 figure.

An examination of the decennial rates of increase since 1790 indicates that during each of the seven decades up to 1860 the population increased by approximately one-third. On the basis of an estimated correction made for the apparent underenumeration in 1870, the percentage increases for the decades 1860 to 1870 and 1870 to 1880 become, respectively, 26.6 and 26.0 rather than 22.6 and 30.1. (See footnote 3 of table 2.) On the basis of these revised figures, the decennial rates of increase for the period 1860 to 1890 were all in the neighborhood of 25 percent.² The decennial rates of increase in the period 1890 to 1910 were about 20 percent, and those for the period 1910 to 1930, about 15 percent. The percentage increase for the period 1930 to 1940, the decade of the depression, represents an all-time low.

The "center of population" is defined by the Bureau of the Census as that point which may be considered as the center of population gravity of the United States; in other words, the point upon which the United States would balance, if it were a rigid plane, without weight and the population were distributed thereon with each individual being assumed to have equal weight and to exert an influence on a central point proportional to his distance from that point. Table B and figure 10 give the approximate location of the center of population for conterminous United States at each census from 1790 to 1960.

Table B. Center of Population: 1790to 1960

Census year	North latitude			West longitude			Approximate location
United States	°	'	"	°	'	"
1960	38	35	58	89	12	35	In Clinton County, Ill., 6 1/2 miles northwest
1950	38	48	15	88	22	8	3 miles northeast of Louisville, Clay County. Ill.
Conterminous United States
1960	38	37	57	88	52	23	4 miles east of Salom, Marion County, Ill.
1950	38	50	21	88	9	33	8 miles north-northwest of Olney, Richland County, Ill.
1940	38	56	54	87	22	35	2 miles southeast by east of Carlisle, Haddon township, Sullivan County, Ind.
1930	39	3	45	87	8	6	3 miles northeast of Linton, Greene County, Ind.
1920	39	10	21	86	43	15	8 miles south-southeast of Spencer, Owen County, Ind.
1910	39	10	12	86	32	20	In the city of Bloomington, Ind.
1900	39	9	36	85	48	54	6 miles southeast of Columbus, Ind.
1890	39	11	56	85	32	53	20 miles east of Columbus, Ind.
1880	39	4	8	84	39	40	8 miles west by south of Cincinnati, Ohio (in Kentucky)
1870	39	12	0	83	35	42	48 miles east by north of Cincinnati, Ohio
1860	39	0	24	82	48	48	20 miles south by east of Chillicothe, Ohio
1850	38	59	0	81	19	0	23 miles southeast of Parkersburg, W. Va 1
1840	39	2	0	80	18	0	16 miles south of Clarksburg, W. Va 1
1830	38	57	54	79	16	54	19 miles west-southwest of Moorefield, W. Va.1
1820	39	5	42	78	33	0	16 miles east of Moorefield, W. Va.1
1810	39	11	30	77	37	12	40 miles northwest by west of Washington, D.C. (In Virginia)
1800	39	16	6	76	56	30	18 miles west of Baltimore, Md.
1790	39	16	30	76	11	12	23 miles east of Baltimore, Md.

¹West Virginia was set off from Virginia Dec. 31, 1862, and admitted as a State June 19, 1863.

The center of population of the United States moved westward within the State of Illinois between 1950 and 1960. The 1900 center of population is located about 50 miles east of East St, Louis and about miles northwest of Centralia, in Meridian Township, Clinton County, Ill. The 1960 center is located at latitude 38°35'58" North and longitude 89°12'35" West.

The new center of the United States is 10% miles south and 57 miles west of the 1950 center of the then 48 States, which was located near Olney, Richland County, Ill. Approximately 2 miles of the southward movement and 18 miles of the westward movement is due to the addition of Alaska and Hawaii as States. The remainder of the change resulted from shifts in the population of the 48 States. This westward movement of the center of population between 1950 and 1960 is the greatest during the present century and exceeds all movements westward since the decade of 1880 to 1890. The longest movement westward was during the decade from 1850 to 1860 when the center advanced 80,6 miles. The shortest movement westward was during the decade from 1910 to 1920 when it advanced only 9.8 miles. The point farthest north was the 1790 location, and the point farthest south, the 1960 location; but the difference is only 47 miles. The total westward movement from 1790 to 1960 was 701 miles.

The position of the "center of area," that is, the point on which the surface of the United States would balance if it were a plane of uniform weight per unit of area, is located in Butte County, South Dakota (approximate latitude 44°58' North, longitude 103°46' West).