William Cowper (28 December 1778 – 6 July 1858) was an English-born Anglican cleric in Australia who was the Archdeacon of Cumberland.
His departure from England was delayed by the death of his wife, then the mother of three sons, including Charles, later a leading politician, and one daughter.
He found the state of morality in Sydney deplorable and actively set to work by preaching and, by example, to bring about an improvement.
In 1842 Cowper's eyesight began to fail; he obtained leave of absence to go to London to have an operation and was presented with a purse of £780 by his parishioners to cover his expenses.
In 1849 he had a dangerous illness but recovered, and in 1852 was appointed to administer the diocese during the absence of Bishop Broughton on a visit to England.
In 1812 he had suffered from some form of rheumatic fever, probably contracted in the gaols, and his slow recovery marked the beginning of a life of constant ill health.
Reports of this ill health were made in 1818 and 1829 by William Grant Broughton, Marsden and Darling, but it was not until February 1842 that the formation of cataracts on both eyes compelled him to take leave and return to England for treatment.