William Clancy (12 February 1802 – 19 June 1847) was an Irish Roman Catholic missionary in the United States and British Guiana.
The son of a farmer, William Clancy was born in West Cork and educated at St. Patrick's, Carlow College in Carlow, and St Patrick's College, Maynooth. He was ordained to the priesthood at Maynooth on 24 May 1823. He then served as a curate until 1829, when he became a professor of theology at St. Patrick's, Carlow.
John England, Bishop of Charleston, South Carolina, had been appointed as the Pope’s Legate to the Government of Haiti. Due to the additional responsibilities, England requested assistance. On 30 October 1834 Clancy was appointed Coadjutor Bishop of Charleston, South Carolina and Titular Bishop of Oreus by Pope Gregory XVI.
He received his episcopal consecration on the following 21 December at the Cathedral of the Assumption, Carlow, from Bishop Edward Nolan, with Archbishop Michael Slattery and Bishop William Kinsella serving as c