It's no secret that millions of Americans have British roots — 25 million claim English ancestry, 5 million Scottish, 4 million Scots-Irish and 2 million Welsh, according to the US census. But if you count yourself among that group, your past may be a mystery. Most of those ancestors immigrated so long ago that we often don't know much about them. In fact, many of the 20 million people who identify themselves as simply “American” probably have some British ancestry, too, though they may be several generations removed from their immigrant ancestors.

Today we think of England, Scotland and Wales (and Northern Ireland) as one entity — the United Kingdom — but emigration from these three nations hasn't always followed the same pattern. England supplied the majority of the original Colonies' settlers, beginning with Jamestown in 1607 and Plymouth in 1620, and continuing to the early years of American independence. Large-scale immigration from Scotland began in the 18th century, and from Wales in the 19th century. Still, their stories are intrinsically linked, and you'll follow similar steps to trace your English, Scottish or Welsh roots.