When Does "Long Day's Journey Into Night" (1956) Take Place?
"Long Day's Journey Into Night" is a historical fiction stageplay written by Eugene O'Neill first performed February 2nd, 1956. So when is "Long Day's Journey into Night" set?
It takes place in the year:
We know this because very early on in act 1 Edmund Tyrone says, "He was delighted because he'd had a fight with your friend, Harker, the Standard Oil millionaire"... It has been reported that Harker is based on the real-world philanthropist (and recipient of Standard Oil money) Edward Harkness (1874-1940) so it is most likely before January 29th, 1940 AD when Harkness died. Also, in act 1 Mary Tyrone bemoans, "There go the Chatfields in their new Mercedes. It's a beautiful car, isn't it? Not like our secondhand Packard." The Packard Motorcar Company produced its first automobile on November 6th, 1899 AD. So it is most likely before 1940 AD and must be after 1899 AD.

1912 AD
We know this because very early on in act 1 Edmund Tyrone says, "He was delighted because he'd had a fight with your friend, Harker, the Standard Oil millionaire"... It has been reported that Harker is based on the real-world philanthropist (and recipient of Standard Oil money) Edward Harkness (1874-1940) so it is most likely before January 29th, 1940 AD when Harkness died. Also, in act 1 Mary Tyrone bemoans, "There go the Chatfields in their new Mercedes. It's a beautiful car, isn't it? Not like our secondhand Packard." The Packard Motorcar Company produced its first automobile on November 6th, 1899 AD. So it is most likely before 1940 AD and must be after 1899 AD.
More specifically, James Tyrone says, in act 1 at the very beginning of the play, "I've the digestion of a young man of 20, if I am 65." Then in act 4 he reveals, "In 1874, when Edwin Booth came to the theater in Chicago where I was leading man"... "And I was only 27-years-old!"
65 - 27 = 38
and
1874 + 38 = 1912.
Furthermore, the stage directions declare it is "a morning in August, 1912." The entire story covers just one day so presumably it's entirely within August of 1912 AD.
It has also been reported O'Neil heavily based the story on his own adolescent experience.
It was adapted to film in 1962, as a television movie in 1982, another TV movie in 1987, then again as a film in 1996, and another film in 2025.