Which of these U.S. TV series debuted first?

With the four TV series in this instance, the one that debuted first was "The Waltons" (1972–1981). This series ran 221 episodes. It concerns the life and trials of a 1930s and 40s Virginia mountain family through financial depression and World War II. It is a show that was created by Earl Hamner Jr., based on his 1961 book "Spencer's Mountain". Key members of the cast include Richard Thomas, Ralph Waite, Michael Learned, Will Geer, and Ellen Corby. The story is set in Walton's Mountain, a fictional mountain-area community.

"Little House on the Prairie" (1974–1982) is a TV series that premiered on the NBC network. It is made up of 204 episodes. Based on Laura Ingalls Wilder's series of "Little House" books, the TV drama series revolved around the 1870s adventures of the Ingalls family. The key stars are Melissa Gilbert, Michael Landon, Karen Grassle, and Rachel Lindsay Greenbush.

"Dr. Quinn, Medicine Woman" (1993–1998) is a TV series of 150 episodes that ran on CBS for 6 seasons. It is a Western drama series that was created by Beth Sullivan, starring Jane Seymour as a physician who leaves Boston in search of adventure in the Old American West and settles in Colorado Springs, Colorado.

"Touched by an Angel" (1994–2003) is a fantasy drama TV series that premiered on CBS and ran for 211 episodes. It was created by John Masius and stars Roma Downey and Della Reese. Throughout the series, the ladies as angels are tasked with bringing guidance and messages from God.