He married Elizabeth Fairburn on 27 April 1843. William and Elizabeth Colenso worked at the Waitangi (Ahuriri, Napier) Mission from 1844. In the 1840s, from his mission station in Hawke's Bay, Colenso made several long exploratory journeys through the central North Island in the company of Maori guides with the aim of reaching the inland Maori settlements of Patea, in the Taihape region, and converting them to Christianity. His travels took him through trackless forest, over the high Ruahine Range and across the Rangipo Desert and past the mountains of Ruapehu and Tongariro to the shores of Lake Taupo. His use of existing Maori routes into the interior contributed greatly to the European exploration of the central North Island. One of his journeys, between December 1841 and February 1842, was across the North Island and up to the Kaipara Harbour.