A police spokesperson for the Harris County Sheriff in Indiana tells ET that they received a 911 call in reference to an unresponsive female on Saturday, and that first responders found Moran deceased upon arrival. An autopsy is still pending.
Moran shot to fame in the '70s as Joanie Cunningham on Happy Days, the younger sister of Ron Howard's Richie Cunningham. She later went on to star in her own spinoff, Joanie Loves Chachi, based on her character's relationship with Chachi Arcola, played by Scott Baio.
Throughout the next several decades, Moran starred on The Love Boat, and had appearances on Murder, She Wrote and Diagnosis Murder.
"I am so incredibly sad to hear about Erin. She was a wonderful, sweet, caring, talented woman. As I write this I can't really comprehend this right now. A very painful loss. It gives me some comfort to know that she's with Tom, Al, Pat and Garry. Rest in peace, sweet Erin," Moran's former Happy Days co-star, Don Most, said in a statement to ET, while Anson Williams added, "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."
Baio remembered the actress on Facebook, writing, "May people remember Erin for her contagious smile, warm heart, and animal loving soul. I always hoped she could find peace in her life. God has you now, Erin."
"I am so, so sad to hear this. She was just a sweet, bright, bubbly, fun person. She brought joy to millions," said Moran's friend and fellow child star, Alison Arngrim.
Cathy Silvers, who played Jenny Piccalo on Happy Days, remembered Moran as her "best friend," "shining armor," and "my example of unconditional love, grace, poise, dignity, strength, [and] talent beyond measure" in a statement to ET.
"Above all, Erin held my hand throughout my life," Silvers added. "My love for Erin is forever. A beautiful person, no luckier woman than I to call Erin my loving best friend. When the casting door opened, and I walked in and jumped on the couch to read for Jenny Piccalo, we laughed our heads off. Then Erin threw her arms around me and our journey of friendship began. We were very close on set and grew even closer now. May we all be as gracious, elegant, respectful, kind and unconditionally loving as Erin Moran. 'Jones!!! We will meet again my friend and the trouble we will cause will be exponential!' xoxo."
ET also spoke to actress Marion Ross -- who played Moran's mother on Happy Days -- who told us she was "devastated" at Moran's death.
"She was so cute and bright and great on the set of our show," Ross recalled. "We would send her off to school and she would come back to the set and pick right up on what she had to do! She was so adaptable, so talented. She got cuter and cuter every year!
"In 2007, dear Florence Henderson and her daughter, Susan, Erin and I christened the Love Boat cruise ship in Athens, Greece," she added. "Again, I am devastated, but I will always remember Erin."