William Day (1529 – 20 September 1596) was Bishop of Winchester (1595–96), Dean of Windsor (1572–95), and Provost of Eton College (1561–95).

[2] He became a fellow of Eton College in 1560, and in 1561, after Richard Bruerne resigned, he was elected to be Provost, a position he held until 1595.

[2] Day was recommended to be a bishop by numerous figures, including Matthew Parker, William Cecil, John Aylmer, and John Whitgift, from as early as 1568.

[2] George Day, Bishop of Chichester, was his elder brother.

William had converted to Protestantism, but George remained Catholic, which caused a rift between the two brothers.