Kenneth L. Heisterkamp, 85, of Rapid City, died December 4, 2025, at the Monument Health Hospice House.

Ken was born September 1, 1940, in Breda, IA, to Leo A. Heisterkamp and Leonella (Wess) Heisterkamp. He graduated from St. Bernard Grade and High School in Breda. He then attended college at the University of South Dakota and received his bachelor's degree in 1962 and his law degree in 1964.

He married Marlene Tiefenthaler at St. Bernard's Church in Breda, IA, in 1962, and together they had three children, Sheri Manderle, Brian Heisterkamp, and Tracie Heisterkamp; five grandchildren, Brandon, Luke, and Logan Manderle, and Joshua and Isabella Heisterkamp; and three great-grandchildren, Jackson, Emmalyn, and Melanie Manderle.

Ken was a law clerk to federal judges Mickelson and Beck, and upon completing his clerkship joined the Hanley, Costello, Porter law firm in 1965 (the firm now known as Costello, Porter, Hill, Heisterkamp, Bushnell & Carpenter). Ken retired from the firm as a fulltime partner in January 2001 but continued on as of council to the firm for several years thereafter. Ken was past president of the Pennington County Bar Association, a member of the South Dakota Code Commission, and of the South Dakota Bar Commissioners.

He enjoyed golf but he always said he knew how to play the game better than he played it. He also enjoyed cooking which he once said may explain any rumor that he may have died from food poisoning. He will be remembered for his sense of humor and he thoroughly enjoyed a good laugh. He enjoyed reading, especially biographies and books on famous war battles and also watching and watching and watching the movie Patton.

Ken is survived by his wife, Marlene, their three children: daughter Sheri Manderle (her husband Jim and their three children Brandon, Luke, and Logan, great-grandson Jackson and great-granddaughters Emmalyn and Melanie), son Brian Heisterkamp (his partner Auturo Cabello and their children Joshua and Isabella), and daughter Tracie Heisterkamp. Also surviving are his siblings Jayne Koster and Shirley Longacre.

Preceding him in death are his parents, brother Howard (Butch) Heisterkamp, and sister Bonnie Henrich.

A visitation will be hosted at Osheim & Schmidt Funeral Home on Monday, December 8, 2025, from 5:00 p.m. to 6:00 p.m. with a Vigil Service at 6:00 p.m.  A Christian Funeral Mass will be held at Blessed Sacrament Catholic Church on Tuesday, December 9, 2025, at 10:00 a.m. with burial to follow at Mt. Calvary Cemetery.