Gross was born in Middletown, Ohio, the son of Shirley (Tait), a homemaker, and Sewell Mark Gross, a sales executive for AK Steel Holding. Part of his family is originally from Winnipeg, Canada. He was raised a Presbyterian.He moved with his parents to San Francisco in 1954.
Gross is married to Sue J. Gross. They have one child together and Bill has two children from a previous marriage.