Rédemptoristes
Willem van Rossum was born in Zwolle, Netherlands, to Jan and Hendrika (née Veldwillems) van Rossum. He entered the Minor Seminary of Culemborg in 1867 and joined the Congregation of the Most Holy Redeemer, more commonly known as the Redemptorists, on 15 June 1873. He made his profession as a Redemptorist on 16 June 1874.