As M*A*S*H continued to be a rating's smash, and the series continued on into the years, creative license had to be practiced regarding the series' timeline - especially considering the series ended up lasting nearly three times as long as the actual Korean War. Because of this, it's not unusual for episodes from earlier seasons to take place in the year 1952, or later seasons taking placing in 1950 or 1951.

Few episodes contain actual dates, or references to historical events that indicate when in time the story takes place. Using these references provides a list below of episodes taking place in order according to the timeline of the 4077th's involvement with the Korean War:

# Episode Title Known Dates Comments
1x01 "Pilot" Summer 1950 On screen caption dates the episode as 1950. War broke out June 25, 1950, and given that Hawkeye receives a letter from the dean of his alma mater, informing him that the college is willing to accept Ho-Jon in the fall, would probably set the episode sometime mid or late summer in 1950.
7x03 "Lil" September 10, 1950 After Margaret converses with Colonel Lillian Rayburn about the freedoms of single life for women, she tries sharing her new perspective with Klinger, by informing him it's Independence Day, to which Klinger sarcastically points out the date as September 10th.
2x11 "Carry On, Hawkeye" October 1950 News over the P.A. reports Ralph Bunche winning the Nobel Peace Prize for his work on an armistice agreements between Israel and the Arab states in 1948-1949; announcement for Nobel Peace Prize winners were usually in mid-October.
1x12 "Dear Dad" December 1950 Hawkeye writes to his father about the Christmas festivities (or lack thereof) at the 4077th, including Henry's sex lecture, Trapper delivering a calf, Frank and Klinger's scuffle in Post-Op, and going out into the field dressed as Santa.
8x25 "April Fools" April 1, 1951 Potter tries to keep the camp from engaging in any practical jokes on April Fools Day while other brass is visiting.
2x04 "For the Good of the Outfit" May 1951 After Hawkeye spends a great deal of time getting the U.S. Army to take responsibility for bombing the village of Tai-Dong, he finally receives a response from his father in the mail, dated May 24, 1951.
7x24 "A Night at Rosie's" August 9-10, 1951 The morning after spending all day at Rosie's Bar, a drunken solider finally awakens, noting the last thing he remembers is toasting July 4 with his buddies in Honolulu, and that he joked he wanted to join the fun in Korea (which his buddies evidently took seriously). B.J. informs him that the current date is August 10th, which would mean the majority of the episode took place the day before.
7x11 "Point of View" September 11-13, 1951 Private Rich's second night in Post-Op dates a letter he's writing home to his parents as September 12, 1951; this would date his injury and arrival at the 4077th as September 11, and waking up the following morning for his fractured larynx as September 13.
5x01, 5x02 "Bug Out" September 21, 1951 This date is not confirmed. Margaret mentions in passing that this episode takes place in September; following the previous season's initiative that the episode airdates coincide with the dates of the events taking place in camp, one could assume that "Bug Out"'s airdate of September 21, 1976 could coincide with the bug out itself taking place September 21, 1951. The year 1951 is stated when Hawkeye observes the date on Radar's bottle of Grape Nehi.
2x03 "Radar's Report" October 17-22, 1951 Radar types up the weekly report for HQ, dating the report for the week of October 17, 1951, which would span this episode's timeline through the 22nd. The events that Radar reports include a wounded Chinese prisoner contaminating Trapper's patient's I.V., developing complications and eventual death, Hawkeye tending to the wounds of new nurse Erika, and a Section 8 evaluation for Klinger conducted by Sidney Freedman (or Milton, in this episode).
7x15 "Dear Sis" December 19-25, 1951 Father Mulcahy begins his letter to his sister the week before Christmas, which would indicate the events he writes about - including his contributions to Sister Teresa's Orphanage Fund, blessing the birth of the O'Reilly farm's new calf, Margaret and Klinger sulking over their divorces, Charles depressed over his first Christmas away from home, and accidentally punching a rude casualty - span the 19th up to the 25th of December.
9x05 "Death Takes a Holiday" December 25, 1951 A fatally wounded soldier is brought into camp, and B.J. tries desperately to prolong his death so his children won't have to think of Christmas as the day their father died. His attempts prove futile, but Hawkeye changes the clock to make the time of death 12:05am December 26th.
9x06 "A War for All Seasons" December 31, 1951 The 4077th has a New Year's Eve party, and reflects on the events of the previous year in flashback.
5x15 "The Most Unforgettable Characters" June 13, 1952 Radar dates the daily staff duty log he types as June 13, 1952. Frank's birthday also takes place on the same day, which would contradict the birthday party thrown for him in the dead of winter in "For Want of a Boot."
6x11 "The M*A*S*H Olympics" July or August 1952 The Olympics in Helsinki, Finland were happening during the episode.
3x24 "Abyssinia, Henry" August 1952 The year 1952 is explicitly stated when Radar presents Henry with his engraved key chain. While the exact date would be difficult to determine, it can be guessed that Henry's discharge took place no earlier than August; see the comments for the following episode:
4x01, 4x02
"Welcome to Korea"
September 12, 1952 The date September 12, 1952 is given over the P.A. system at the opening of the second part of the episode in syndication (which would coincide with the original hour-long episode's airdate of September 12, 1975). This means this is the date that Trapper departs for home, while B.J. arrives in camp: prior to Trapper's departure, he gets drunk for three days straight; Trapper's drunken celebration happens through Hawkeye's week of R&R, which means he would have left for Tokyo September 5. At the same time, Frank Burns clearly hasn't been in command of the 4077th too long - perhaps a week at least - which would indicate the events of "Abyssinia, Henry" took place in late August.
4x03 "Change of Command" September 19, 1952 The P.A. announcement during the closing tag of "Welcome to Korea" gives the date of Potter's arrival as the 4077th's new commanding officer as September 19, 1952 (which coincides with the episode's original airdate of September 19, 1975). Later in "The Bus," B.J. supports the passage of time when he reminds Frank that he spent a week with him in command.
7x04, 7x05 "Our Finest Hour" October 9, 1952 War Co-respondant, Clete Roberts, opens his documentary on the 4077th with the date of October 9, 1952, which would coincide with the original hour-long episode's airdate of October 9, 1978.
4x21 "The Novocaine Mutiny" Late October 1952 Hawkeye's court martial trial takes place after the week of October 5-11, 1952, which is when Frank would have been in temporary command while Potter is away on R&R; knowing Frank, he probably would have pressed charges against Hawkeye immediately, and see that he was tried as soon as possible.
7x20 "Hot Lips is Back in Town" December 1952 It is a possibility this episode took place during December 1952, as that a calendar page for that month and year can be seen in the Nurses' tent when Radar finally asks Linda Nugent out.
10x10 "Twas the Day After Christmas" December 25-26, 1952 The episode opens on the night of Christmas, where visiting British soldiers Major Cass and Sergeant Barnstable share the details of this Boxing Day tradition of officers and enlisted men switching positions with Potter, who is inspired to initiate the tradition for the 4077th the following day.
6x01, 6x02 "Fade Out, Fade In" Spring 1953 While no actual date for this episode is given, Klinger tells "Captain" Schaffer that he will have been wearing dresses and bucking for a Section 8 for exactly two years as of April 22. Given that the war broke out in the summer of 1950, it can be verified that Klinger was drafted, shipped out, and assigned to the 4077th prior to April 22, 1951. Likewise, the information could suggest this episode takes place early in the spring of 1953.
11x16 "Goodbye, Farewell, and Amen" July 4-28, 1953 Hawkeye tells Sidney that on July 4, Potter gave the camp the day off, so they had a party on a deserted cove north of Incheon. The truce ending the Korean War was signed on July 27, 1953, and the ceasefire went into effect that same evening; after a final supper in the Mess Tent, and Klinger and Soon-Lee's wedding the following morning, the personnel of the 4077th go their separate ways.
11x02 "Trick or Treatment" October 31, 1953 The 4077th celebrates Halloween (October 31st) in 1953: this conflicts with the Korean War's end on July 27, 1953.