Evan Ellingson, best known for starring in CSI: Miami and the Cameron Diaz film My Sister's Keeper, has died aged 35.
Ellingson was found dead in the bedroom of a Fontana residence on Sunday, according to the San Bernardino County Sheriff's Department.
The LA Times reported that San Bernandino police said there were no obvious signs of foul play.
A cause of death has not yet been established. A post-mortem was due to take place on Monday.
TMZ first reported the news and spoke to Ellingson's father, who said his son had struggled with substance abuse disorder and had died at a sober living home where he had been staying.
He added that Ellington had been doing well and his death had come as a shock to his family.
Paying tribute, his former co-star Abigail Breslin said: "Evan Ellingson was a kind, funny and extremely talented human being. He played my big brother in a film I did called My Sisters Keeper.
"Evan was a genuinely thoughtful person who cared so much about turning in the best performance, which he accomplished. Some of his scenes in MSK still give me chills.
"He was also silly, funny, a prankster, a lover of Red Bull (I hated the smell of Red Bull) and he was energetic and the life of the party."
Ellingson first found work in commercials as a child, including an advert for clothing and shoe company, Vans.
He landed a regular role in 2000 Fox sitcom Titus and, in 2004, starred in ABC sitcom Complete Savages as Kyle Savage alongside Erik von Detten and Keith Carradine.
In 2007, he landed the role of Josh Bauer in 24 alongside Kiefer Sutherland and then spent three years as Kyle Harmon in CSI: Miami from 2007 to 2010.
Ellingson also worked in films and in 2006 was cast by Clint Eastwood in Letters from Iwo Jima.
His most famous film role came in the 2009 drama My Sister's Keeper alongside Diaz, Breslin and Alec Baldwin.
He played the son of Diaz and Jason Patric's characters.
Ellingson had not appeared on screen in several years.
According to his Facebook page, Ellingson was working for a religious organisation called Teen Challenge South California and his hobbies included surfing, horse riding and hiking.
A tribute re-posted by Ellingson's girlfriend, Kaysha Dial, said that Ellingson had recently relapsed after taking painkillers for dental work.
"Our family is heartbroken by the sudden passing of our beloved son, brother, uncle and friend, Evan," read the post by Victoria Haines-Perez.
"Evan was one of the most caring individuals who loved Jesus with all his heart. He had a sweet, child-like spirit with a smile that could light up a room. He was always thinking of others and wanted to use his own struggles with addiction to help people find hope.
"Evan was three years sober and often shared his journey of recovery through speaking engagements and ministry. He was passionate about pointing individuals to resources for help and only recently relapsed after being prescribed opioids following a dental procedure."