On the arrival of the American missionaries in April 1820, all the chiefs were consulted respecting the expediency of their establishment in the islands. Some of the chiefs seemed to doubt; but Keōpūolani without hesitation approved their proposals. Keōpūolani welcomed them. As the highest ranking ali‘i of her time, her embracing of Christianity set a crucial seal of approval on the missionaries and their god. Later, she was very ill and returned to Lahaina (May 31, 1823), asking missionaries to join her.
Immediately on their arrival, she requested them to commence teaching, and said, also, “It is very proper that my sons (meaning the missionaries) be present with me at morning and evening prayers.” On the last week in August, Keōpūolani had a premonition of her approaching death. She was baptized by William Ellis and died shortly thereafter (September 16, 1823). Keōpūolani is said to have been the first convert of the missionaries in the islands and the first to receive a Protestant baptism. (Kalanimōku and Boki had previously (1819) been baptized by the French Catholics. Kalanimōku later (1825) joined the Protestant Church, at the same time as Ka‘ahumanu.)