The following map depicts the dominant ancestries in each county in the USA based on the US census data from 2000:
A Nation Descended from Immigrants
The majority of the 300 million people currently living in the United States are descended from European immigrants who have arrived in the past 400 years. Most Latin American immigrants are from Mexico and Central America of which about half are descended from indigenous peoples of those regions and Spaniards (mestizo). African American people, most of whom are descended from Africa and the slavery era, form the next-largest ethnic groups. American Indians now form a small minority in the population.
The Mix of European Descendants
Major components of the European segment of the United States population are descended from immigrants from Germany (19.2%), Ireland (10.8%), England (7.7%), Scotland (5.8%), Italy (5.6%), Scandinavia (3.7%) and Poland (3.2%) with many immigrants also coming from other Slavic countries. Other significant European immigrant populations came from eastern and southern Europe and French Canada; few immigrants came directly from France. Since French, French-Canadian and Acadian ancestries are overlapping, the number of counties with “French” as the main ancestry would also be larger if these three labels are added together.
African American Ancestry
A large number of Americans are descended from Africans (12.9%), the majority of whom were brought as slaves as early as the 17th century throughout the 19th century during the Transatlantic slave trade, with smaller numbers having immigrated since then from Africa or the Caribbean. The ancestral national origin of most African Americans has been difficult to trace until recent DNA analyses.
Most African nations were named centuries after slaves were imported the Americas, and most slave owners generally did not keep track of the slaves’ ethnicity. Therefore the continent of Africa serves as an indicator of geographic origin and a descriptive term. African-Americans who know their ethnic origin are generally from post-slave trade era migration such as Barack Obama, who is of Luo Kenyan descent and Hakeem Olajuwon who is Yoruba Nigerian ancestry.