William Kostner Obituary
With solemn hearts, we announce the passing of William Kostner of Mukwonago, Wisconsin, whose presence will be deeply missed, having departed on November 23, 2025 at the age of 80. Leave a sympathy message to the family on the memorial page of William Kostner to pay them a last tribute.
He was predeceased by: his parents, Ervin Kostner and Lorraine Kostner (Soha); his wife Jan; his brother-in-law Al Krause; his nephew David Krause; and his granddaughter Addy May Sieberer.
He is survived by: his daughters, Julie VanDixhorn (Tom) of Birmingham, AL and Katie Sieberer (Andy) of Elkhorn, WI; his grandchildren, Jake, Bailey, Abby, Drew and Camryn; and his niece Jackie Krause Johnson.
In lieu of flowers, the family requests that memorials in Bill's name be made to the University of Sioux Falls Women's Softball Scholarship or the Mayo Clinic Cancer Center and may be directed through the family.
