On 1637 or 1638 Willaerts sailed to Brazil serving in the of Count John Maurice of Nassau-Siegen, the governor of the Dutch possessions in Brazil. In 1641 the Count sent him with the Dutch fleet from Brazil to Angola (where the Dutch had just taken São Paulo de Loanda and the island of Tomé) on a mission to observe the customs and manners of the indigenous people. He had returned to the Netherlands in 1644, where he stayed with the prominent architect and painter Jacob van Campen at his castle Randenbroeck near Amersfoort.