Horton was staying at a Los Angeles nursing home after suffering from a stroke. Her son said she died on Wednesday night.
As a teenager, she formed a band called "The Casinyets," which was short for "Can't Sing Yet," with some friends.
The group later changed its name to The Marvelettes and she became the lead singer. Horton sang on hits such as "Please Mr. Postman."
The tune, more pop-oriented than much of Motown's early recordings, was later covered by the Beatles and others.
The Marvelettes also had a hit with "Beachwood 4-5789." Their other popular songs included "Playboy," "Too Many Fish in the Sea" and "Twistin' Postman."
Horton was replaced as the group's lead singer in 1965, and she left the Marvelettes two years later.
The Associated Press contributed to this report.