It was rare as an American given name before 1975. In the mid-1980s it began growing in popularity for boys after a character by this name began appearing on the soap opera Ryan's Hope. It is now more common as a feminine name, probably due to the fame of the actress Dakota Fanning (1994-).
Very rare as an American given name before 1980, it increased in popularity in the 1980s and 90s. It got a boost in 2004 after the debut of the television series Lost, which featured a character by this name.