This webpage lists the amount it cost the U.S. government to take the Federal Decennial Census for each of the census years 1790-2010...
Census Year Total Population Census Cost Average Cost Per Person
1790 3,929,214 $44,377 1.13 cents
1800 5,308,483 $66,109 1.24 cents
1810 7,239,881 $178,445 2.46 cents
1820 9,633,822 $208,526 2.16 cents
1830 12,866,020 $378,545 2.94 cents
1840 17,069,458 $833,371 4.88 cents
1850 23,191,876 $1,423,351 6.14 cents
1860 31,443,321 $1,969,377 6.26 cents
1870 38,558,371 $3,421,198 8.87 cents
1880 50,155,783 $5,790,678 11.54 cents
1890 62,979,766 $11,547,127 18.33 cents
1900 76,303,387 $11,854,000 15.54 cents
1910 91,972,266 $15,968,000 17.07 cents
1920 105,710,620 $25,117,000 23.76 cents
1930 122,775,046 $40,156,000 32.71 cents
1940 131,669,275 $67,527,000 51.29 cents
1950 151,325,798 $91,462,000 60.44 cents
1960 179,323,175 $127,934,000 71.34 cents
1970 203,302,031 $247,653,000 $1.22
1980 226,542,199 $1,078,488,000 $4.76
1990 248,718,301 $2,492,830,000 $10.02
2000 281,421,906 $4.5 Billion $15.99
2010* 308,745,538 $13 Billion $42.11
The 1940 Census
1940 census records were released on April 2, 2012. For details see:1940 Census Records and Information
The U.S. population reached 300,000,000 on 17 October 2006
Click for "Population Clock". By Feed Digest
Source (except 2010)...
Gauthier, Jason G., Measuring America: The Decennial Censuses From 1790-2000, (US Bureau of the Census/Dept of Commerce), Washington: US Government Printing Office, 2002, Appendix A, Page A-1. The numbers in the fourth column are not included in the book and were added by me.
* The 2010 census cost was taken from GAO (U.S. Government Accountability Office) report number GAO-11-496T, 2010 Census: Preliminary Lessons Learned Highlight the Need for Fundamental Reforms (April 6, 2011): "At about $13 billion, 2010 was the costliest U.S. Census in history." The official census day for 2010 was April 1, 2010. The total population figure (308,745,538) was announced by the U.S. Census Bureau on Dec. 21, 2010. See: 2010 Census - Resident Population Data