The family sailed to America in 1861 on the ship Monarch of the Sea. The ship manifest shows his name as "Jens Thomassen."
He was traveling with his step-father, Parley Thompson, his mother, and siblings. The Thompson family arrived in New York on 16 June 1861 via the ship Monarch of the Sea. The reminiscence of his sister, Martina, infers that the entire family made the overland trip together.