Hi Eleanor, Welcome to Wikitree!!
I googled and found that the last name McCormack comes from Scottish orgins as well as from Ireland.
Info on McCormack migration to the United States can be found here https://www.houseofnames.com/mccormack-family-crest and even some names to look up.
If there is a particular group of McCormacks your interested in, let us know and add some info (if you have a relative named McComack) about what year, they were born, died and any other info you might have to get us started in research. Just post a new inquiry with that info and see if it helps. Our researchers also provide sources for the info they find.