The population of U.S. cities, towns and villages in the U.S. is listed in the blue pages of the print Martindale-Hubbell. More officially, use the Census Bureau's American Factfinder; type "population" in the top box and then the name of the place.
To find out the population of foreign countries, try The World Fact Book, the Library of Congress' Country Studies and/or the Social Indicators page posted by the United Nations Statistical Division. Population data for the major cities and countries of the world is available through the Population Size and Density page posted by the United Nations Statistics Division.
For "summaries and excerpts of legislation, constitutions, court decisions, and other official government documents from every country in the world relating to population policies" check out The Annual Review of Population Law produced jointly by Harvard Law School and the United Nations Population Fund.