Herseth was born in Columbia, South Dakota on April 5, 1909. Her parents, Albert and Ida Yeske Buntrock, were German immigrants. She was the youngest of 11 children. Herseth attended Northern State Teacher's College and earned a teaching credential after two years of study.
She married Ralph Herseth, who served as Governor of South Dakota from 1959 to 1961, on December 23, 1937. They had dated for nine years prior to getting married. Together they had three children, Karen, Connie, and Ralph Lars.
Their son, Ralph Lars Herseth, served in the South Dakota State Legislature. Their granddaughter, Stephanie Herseth Sandlin, served in the United States House of Representatives. Herseth served as mentor to Sandlin. During her life, Herseth lived in Houghton, South Dakota and in Pierre, South Dakota. She was a Lutheran. She died on September 8, 1994 and was buried in Houghton Cemetery.
After college, Herseth taught in the Brown County public schools as well as in urban schools. In 1936, Herseth was elected as Brown County Superintendent of Schools. For seven years, she served on Brown County's Reorganization School Board. She later served on the Selby School Board.
- "Herseth, Lorna B. (1909-1994)". Political Graveyard. August 19, 2019. Retrieved August 19, 2020.
- "The First Ladies of South Dakota" (PDF). South Dakota State Historical Society. 1973. Retrieved August 19, 2020.
- "Calendar marks celebration of 100 years of Buntrocks". Argus-Leader. Sioux Falls, South Dakota. June 13, 1987. p. 5 – via Newspapers.com.
- Adams, Katherine H. (July 1, 2019). Claiming Her Place in Congress: Women from American Political Families as Legislators. McFarland. p. 150. ISBN 978-1-4766-3717-4. Retrieved August 19, 2020.
- "Legacy of Achievement: Hall of Fame Inductee Stephanie". South Dakota Hall of Fame. Retrieved August 19, 2020.