Despite the long history of Hispanic residents in the United States, there was no systematic effort to count this group separately in the Census until the late 20th century. An analysis of changes in Census question wording over recent decades reveals the challenges in trying to count and describe this fast-growing population.
An estimated 48 million Hispanics are now living in the U.S., or almost 16% of the population. Hispanics are the nation's largest minority group, having surpassed African Americans in number in 2001. The growth of the Hispanic population this century is due mainly to births in the United States, not immigration from abroad, a reversal of the pattern over the previous four decades.
Read Jeffrey S. Passel's full commentary Census History: Counting Hispanics on the Pew Research Center's Web site.