According to the 2007 census, it has a population of 289,833 (see above). Its population consists of 70% Catholic, 10% Protestant, 10% atheist and 10% of various sects, including Iglesia ni Cristo, Muslim and others. The people of Cainta are mostly Tagalog-speaking Filipinos.

A considerable number of the population are descended from Indian soldiers who mutinied against the British Army when the British briefly occupied the Philippines in 1762 to 1763. These Indian soldiers called Sepoy settled in town and intermarried with native women. The Sepoy ancestry of Cainta is still very visible to this day, particularly in Barrio Dayap near Brgy. Sto Nino. Their unique physical characteristics make them distinct from the average Filipinos who are primarily of Malay and Chinese origins.