Immigration in America started with the landing of Jamestown, it's been a part of our country since day one. However, after the Revolutionary War we've had a migration of immigrants to the United States. I mention this because there seem to be pockets of time and place where several from one country would settle here in the states.
On a website for Laiden University there's an interesting article about who came when and why. Here's the link
I bring this up because I've used several ethnic groups while writing my historical fiction novels, Corduroy Road to Love is one such example. When researching an area to set a novel in, research the emigration into that community. You might just stumble across some interesting information.
Currently I'm researching the Dutch and German migration to a section of New York where my husband's family find some of their roots. Most of them came as farmers when the opportunity to have their own farm, approximately 100 acres of land, to build their home and futures on.
Below is a short list of some of the Emigrations to America it is not exhaustive but just to give you a quick overview.
British throughout most of the century
European Immigrants to Antebellum US 1840-1860
Irish (Potatoe Famine) 1845-1851
Chinese (Gold Rush California) 1850-1882
Italian 1876 thru 1976
Germans 1830 largest years 1854-1894