Shortly after 4 p.m. ET, Indiana authorities were alerted to a report of an "unresponsive female." Upon arrival on the scene, Moran's body was discovered.
Moran in the "Happy Days" credits
No official cause of death has been released, but DailyMail.com reports it was a "suspected heroin overdose."
Moran starred on the series "Daktari" from 1966 - 1969, and on "Happy Days" from 1974 - 1984. From 1982 - 1983, she starred, along with Scott Baio, on the short-lived spin-off series "Joanie Loves Chachi."
Roles were few and far between following Moran's success on "Happy Days." Aside from several appearances on "The Love Boat," she logged only seven acting gigs, including a self-parodying turn in the film "Dickie Roberts: Former Child Star" in 2003.
Moran as she appeared in 2009
She was a contestant on "Celebrity Fit Club" in 2008, and her final screen appearance was in "Not Another B Movie" (2010).
In 2010, Moran and several of her "Happy Days" co-stars sued CBS over payments they argued they were due on merchandising from the show. They later settled the suit.
In 2012, Moran was reported to be living at near-poverty level, and was said to be writing a memoir.
She is survived by her husband, Steve Fleischmann.
In a statement to "Extra," Henry Winkler — who played The Fonz on "Happy Days" — said, "I will always remember Erin with her sweet smile that greeted me on the very first day I walked onto the set of 'Happy Days' in 1974. She was only nine years old. For the next 10 years, that smile never faded. Unfortunately, yesterday it did. My condolences go out to her family. She will always be locked in my heart."
Moran was also warmly remembered on social media by other co-stars of the show, including director Ron Howard, who played her big brother Richie on the series:
Such sad sad news. RIP Erin. I'll always choose to remember you on our show making scenes better, getting laughs and lighting up tv screens. https://t.co/8HmdL0JKlf
Anson Williams said in a statement: "Erin was a person who made everyone around her feel better. She truly cared about others first, a true angel. I will miss her so much, but know that she is in God's hands. RIP sweet angel."
So incredibly sad to hear about Erin. A wonderful, sweet, caring, talented woman.I can't really comprehend this right now.Very painful loss
Most also said in a statement, "It gives me some comfort to know that she's with Tom, Al, Pat and Garry. Rest In Peace, sweet Erin.” He was referring to Tom Bosley (Mr. Cunningham) who died at 83 in 2010); Al Molinaro (Al Delvecchio) who died at 96 in 2015; Pat Morita (Arnold) who died at 73 in 2005; and series creator Garry Marshall who died last year at 81.