Cook Islanders are Polynesians. Ethnic groups in the 2001 census were: Cook Island Maori, 87.7 percent; part Cook Island Maori, 5.8 percent; other, 6.5 percent. Cook Island Maori belongs to the family of Oceanic languages, a sub-branch of the Austronesian language family. English is the official language while Cook Island Maori is also in use. Among the best educated of the South Pacific Islanders, most Cook Islanders are bilingual, and literate in both languages.
The London Missionary Society introduced Christianity to the Cooks in the early 1800s. In the 1970s, the Cook Islands Christian Church was formed from the London Missionary Society. Cook Islands Christian Church claims 55.9 percent of the population; Roman Catholic Church 16.8 percent; Seventh-day Adventists 7.9 percent; Church of Latter Day Saints 3.8 percent; other Protestant 5.8 percent; other religions 4.2 percent; unspecified 2.6 percent; and three percent say they have no religion.
The languages of the Cook Islands include English, Cook Islands Māori, or "Rarotongan," and Pukapukan. Dialects of Cook Islands Maori include Penrhyn; Rakahanga-Manihiki; the Ngaputoru dialect of Atiu, Mitiaro, and Mauke; the Aitutaki dialect; and the Mangaian dialect. Cook Islands Maori and its dialectic variants are closely related to both Tahitian and to New Zealand Māori. Pukapukan is considered closely related to the Samoan language. English and Cook Islands Maori are official languages of the Cook Islands.