As an adult William drowned in Utah's Jordan River in 1915. The death date given above is the day his body was found (the search for him had lasted for fifteen days).
Ancestry's index to the 1900 census gives the surname "Biler" but it should be "Bills."
Note that his death certificate confirms his death date, but shows his birth date as 5 August 1834. FamilySearch and the inscription on his gravestone show his his birth year as 1835.