William D. Leschensky, 91, of Custer passed away on Saturday, May 16, 2026, at Monument Health Rapid City Hospital. Funeral services will be held at the Custer Lutheran Fellowship on Wednesday, May 20, 2026, at 10:00 a.m., with Pastor Shannon Witt officiating. 

William was born on December 27, 1934, in Waukon, Iowa, to William A. Leschensky and Hazel (Helms) Leschensky. He earned a B.A. in mathematics from Cornell College in 1956 and an M.A. in mathematics from the University of Northern Iowa in 1965. Bill devoted his career to education, teaching high school and college mathematics, serving as the mathematics department chair in several schools, and working in the publishing field as a textbook editor and writer, authoring several mathematics textbooks. Over his career, he received many awards and commendations and was a frequent speaker at mathematics conventions. 

In 1960, he married Sandra Rae Odland at the First Lutheran Church in Clarion, Iowa. The couple lived in Richland Center, Wisconsin, and Wheaton, Illinois, before retiring to Custer. There, they built their home on land west of town and embraced life in the Black Hills. Bill loved fishing, gold panning, chopping firewood, and playing golf at Rocky Knolls Golf Course. He also gave generously of his time to the community, tutoring students in mathematics at the Custer County Library, supporting outreach programs on the Pine Ridge Reservation, and proudly driving his antique car in the Gold Discovery Days parade. 

Bill was a member of the Custer Lutheran Fellowship and deeply appreciated the guidance, support, and friendships he found within his church community. He is survived by his wife, Sandra; his sons, William L. and Paul; and his three grandchildren, Robert, David and Ryan.