Dr George Rippey Stewart (1895-1980) was an American academic and the author of Names on the Land: A historical account of place-naming in the United States. This book was published in 1945 and then reprinted in 1958, 1967, 1972, 1986 and 2008.
In it he considered the influence of many groups on the place-names, including the Scotch-Irish:
The Scotch-Irish in America and the Ulster-Scots in Ulster were indeed proud of that great siege and of the courage and fortitude of the defenders.Also among the non-English immigrants may be counted the Scotch-Irish, who brought with their scanty baggage (as has been said) three things of different worth to the new country - whiskey, the Presbyterian Church, and independence from Great Britain. They were lean fighting-men whose ancestors in Ireland for three generations had known what it was to face 'the wolf and the wood-kern.' A shrewd Pennsylvania governor settled them beyond the Germans, 'as a frontier, in case of any disturbance.' Also they settled in New England far to the north, along the Merrimack. Since they spoke English, though with a little northern burr, they established no new habit of naming, and took over the ways the English had already begun. Moreover, they were not a very sentimental people, and of one name alone they seem to have been proud. That was of the city they had held through one of the famous sieges of history, until at last King William's ship broke the boom, and came sailing up Lough Foyle. The young man who saw those ships from the cathedral tower and fired a gun to signal the relief came years later as Pastor McGregor to settle in New Hampshire, and the town there too was named Londonderry. That same name or its shortened form Derry was scattered across Pennsylvania and even farther west - in that name was the glory of the Scotch-Irish.