He was 88.
The actor died in his sleep at his home in Brentwood, Calif., according to his business manager, Ginny Fazer.
Arness' official website posted a letter from Arness on Friday that he wrote with the intention that it be posted posthumously: "I had a wonderful life and was blessed with some many loving people and great friends," he said.
"I wanted to take this time to thank all of you for the many years of being a fan of Gunsmoke, The Thing, How the West Was Won and all the other fun projects I was lucky enough to have been allowed to be a part of. I had the privilege of working with so many great actors over the years."
As U.S. Marshal Dillon in the 1955-75 CBS Western series, Arness created an indelible portrait of a quiet, heroic man with an unbending dedication to justice and the town he protected.
The wealth and fame Arness gained from "Gunsmoke" could not protect him from tragedy in his personal life: His daughter and his former wife, Virginia, both died of drug overdoses.
Arness, a quiet, intensely private man who preferred the outdoor life to Hollywood's party scene, rarely gave interviews and refused to discuss the tragedies.
"He's big, impressive and virile," co-star Amanda Blake (Miss Kitty) once said of Arness, adding, "I've worked with him for 16 years, but I don't really know him."
The actor was 32 when friend John Wayne declined the lead role in "Gunsmoke" and recommended Arness instead. Afraid of being typecast, Arness initially rejected it.
"Go ahead and take it, Jim," Wayne urged him. "You're too big for pictures. Guys like Gregory Peck and I don't want a big lug like you towering over us. Make your mark in television."
