Wilhelmus Demarteau, M.S.F. (24 January 1917 - 5 December 2012) was a Dutchprelate of the Roman Catholic Church. He was one of the oldest Roman Catholic bishops and Dutch bishops.
Demarteau was born in Horn, Netherlands and ordained a priest on 27 July 1941 for the Congregation of Missionaries of the Holy Family. Demarteau was appointed Vicar Apostolic of the Diocese of Banjarmasin on 6 January 1954 along with Titular Bishop of Arsinoë in Cypro and was consecrated bishop on 5 May 1954. He was appointed bishop of the Diocese of Banjarmasin and served until his resignation on 6 June 1983. Demarteau died on 5 December 2012 in Suaka Insan Hospital (Rumah Sakit Suaka Insan:Indonesian)