Hillbilly is a term for people who dwell in rural, mountainous areas in the United States, primarily in the Appalachian region and Ozarks. As people migrated out of the region during the Great Depression, the term spread northward and westward with them.
The Hatfield clan (1897)
"Hillbilly shot glass" inscribed on a wooden shot glass at a gift shop in Nashville, Indiana.
Buddy Ebsen and Irene Ryan from The Beverly Hillbillies in 1970
Migrant family from Arkansas playing hill-billy songs (1939)
Scotch-Irish Americans are American descendants of Ulster Scots people who emigrated from Ulster to America during the 18th and 19th centuries. Their ancestors had originally migrated to Ulster mainly from the Scottish Lowlands and Northern England in the 17th century. In the 2017 American Community Survey, 5.39 million reported Scottish ancestry, an additional 3 million identified more specifically with Scotch-Irish ancestry, and many people who claim "American ancestry" may actually be of Scotch-Irish ancestry.
An example, showing the usage of Scotch as an adjective, in the 4th edition of Encyclopædia Britannica, Edinburgh, Scotland (1800), and modernized to Scottish in the 7th edition (1829).
Scotch-Irish-American boy in Hawaii, 1909