Analysis of birth records shows that in 2002 almost one in four births in the United States was to an immigrant mother, legal and illegal, the highest level in American history. The enormous number and proportion of children from immigrant families may overwhelm the assimilation process, making it difficult to integrate these new second-generation Americans. At present, the U.S. government automatically gives American citizenship to all people born in the country, even the children of tourists and illegal aliens. Includes statistics on births to immigrant and native mothers, 1990 and 2002, by county and MSA.