As an English name, it became popular due to the Fleetwood Mac song Rhiannon (1976), especially in the United Kingdom and Australia.
This name was common in Sweden and Denmark in the 1970s [1]. It rose in popularity in the English-speaking world in the 1990s, entering the top ten for girls in the United States in 2009. It was also popular in many other countries at that time. Famous bearers include American actress Mia Farrow (1945-) and American soccer player Mia Hamm (1972-), birth names Maria and Mariel respectively.
Due to the popularity of the saint, the name became common in the Christian world during the Middle Ages. The Normans brought it to England, where it was commonly spelled Cecily — the Latinate form Cecilia came into use in the 18th century.