Chronology of Catholic Dioceses:Notes on the Diocese of Winchester, 635 - 1560
The dioceses of Winchester and Sherborne were detached from Dorchester in 635. The two new dioceses were in a personal union until 676, when the separation was made effective.
From 1531, when Stephen Gardiner died, the diocese was vacant due to the Reformation until 1556 when the last Catholic bishop, John White, was installed. He died in 1560, and the diocese then became extinct.
(Source: Catholic Encyclopedia, http://www.newadvent.org/cathen/15649c.htm)
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