Encyclopedias are great for:
Statistical Abstract of the United States. Standard annual summary of statistics on the social, political and economic organization of the United States. A fabulous statistical reference and guide to other statistical publications and sources.
The Oxford Companion to United States history. Oxford University Press, 2001.
American National Biography Outstanding resource on biography and prominent Americans.
Dictionary of American history. A classic ten volume encyclopedia.
Encyclopedia of American Cultural & Intellectual History. New York: Charles Scribner's Sons, 2001. (Olin Library Reference E169.1 .E624x 2001).
Encyclopedia of American Social History. 3 vols. New York: Scribner's, 1992. (Olin Reference HN 57 .E56 1992).
Encyclopedia of American Political History. 3 vols. New York: Scribner, 1984. (Uris and Olin Reference E 183 .E56).
St. James Encyclopedia of Popular Culture. 5 vols. Detroit, MI: St. James Press, c2000.
Encyclopedia of the United States in the Twentieth Century. 4 vols. New York: Charles Scribner's Sons, 1996. (Olin Reference E740.7 .E56 1996).
Encyclopedia of American foreign policy. Thomson/Gale, 2002. 2nd ed.
Encyclopedia of American Religions. Detroit: Gale, 1987. (Olin Reference BL2530.058 M52+ 1987).
Encyclopedia of African-American Culture and History. 5 vols. New York: Macmillan Library Reference, 1996. (Olin and Africana Reference E 185 E54 1996).
The Encyclopedia of Civil Rights in America. Armonk, NY: Sharpe Reference, 1998. 3 volumes. (Olin Reference E185.61 E544x 1998).