Slap in the Maritimes, New York above the Hudson Highlands, the northern third of Pennsylvania (Wyoming Valley then westward), and New Connecticut/the Western Reserve, possibly to the Wabash River.
Those are the first areas settled by an expanding New England (Maritimes in the 1760s, northern PA in the 1770s, upstate NY in the 1780s, and the Reserve in the 1790s) and probably the closest of the Yankee exodus to both have connections to New England in modern political, economical, and cultural ways as well as the nearest geographically.
From those areas, Yankees went on to pretty much settle all Michigan/Wisconsin/Minnesota, the northernmost slice of Iowa, the northern thirds of Indiana/Illinois, the eastern and northern parts of the Dakotas, the northern half of Montana, the northern two-thirds of Idaho, and the Pacific from Monterey northwards as well as being the main force of Americans in Hawaii. But once you get past Ohio you're seeing these areas gradually subsumed into what we think of as subcultures on their own (even if the New Englanders provided the majority, if not vast majority, of their genetic roots): 'the Midwest/Great Lakes', 'the Plains', 'the Rocky Mountains', 'the Pacific Northwest', etc. etc.
Mormons were originally New Englanders as well and it shows in many ways, tho' no one denies in a real way they became their own cultural sect.