The surname Nilsen is derived from the Scandinavian personal name Njáll. This name has the same origin as the Gaelic name Niall, which was adopted by Scandinavian settlers in Ireland. Over time, the forms Niels and Nils developed and the patronymic suffix "sen," or "son," meaning 'son of' was added.
^ Filby, P. William, Meyer, Mary K., Passenger and immigration lists index : a guide to published arrival records of about 500,000 passengers who came to the United States and Canada in the seventeenth, eighteenth, and nineteenth centuries. 1982-1985 Cumulated Supplements in Four Volumes Detroit, Mich. : Gale Research Co., 1985, Print (ISBN 0-8103-1795-8)