<P> 2 . The number of foreign born in 1830 and 1840 decades are extrapolations . </P> <P> Starting in 1820, some federal records, including ship passenger lists, were kept for immigration purposes, and a gradual increase in immigration was recorded; more complete immigration records provide data on immigration after 1830 . Though conducted since 1790, the census of 1850 was the first in which place of birth was asked specifically . The foreign - born population in the U.S. likely reached its minimum around 1815, at approximately 100,000 or 1% of the population . By 1815, most of the immigrants who arrived before the American Revolution had died, and there had been almost no new immigration thereafter . </P> <P> Nearly all population growth up to 1830 was by internal increase; around 98% of the population was native - born . By 1850, this shifted to about 90% native - born . The first significant Catholic immigration started in the mid-1840s, shifting the population from about 95% Protestant down to about 90% by 1850 . </P> <P> In 1848, the Treaty of Guadalupe Hidalgo, concluding the Mexican War, extended U.S. citizenship to approximately 60,000 Mexican residents of the New Mexico Territory and 10,000 living in California . An additional approximate 2,500 foreign born California residents also become U.S. citizens . </P>

Immigrants to the united states between 1840 and 1860 rarely settled in which region