M*A*S*H
M*A*S*H is the 1st TV series to hold the record for the most-watched telecast of all time for decades until 2010's Super Bowl XLIV edged it out with 106 million viewers, which coincidentally also aired on CBS. However, M*A*S*H's final episode remains the all-time most-watched U.S. television episode
Cheers OR One for the Road
Cheers Titled "One for the Road" is the 2nd most-watched series finale in U.S. television history in 1993 finale of the NBC comedy Cheers, titled "One for the Road". It was watched by between 80.4 million and 93.5 million viewers while drawing 64% of TVs turned on at the time.
Seinfeld's
Seinfeld's is the 3rd and 4th most-watched U.S. TV series finale in television history Seinfeld's controversial 1998 episode "The Finale" was watched by 76.3 million people, drawing 67% of all televisions turned on at the time as the New York Times put it, "grazing Super Bowl country" in terms of viewership.
Friends & Magnum, P.I.
Friends & Magnum, P.I. both are the 5th and 6th most-watched TV series finales in television history respectively, those of the comedy Friends (2004, NBC, 65.9 million viewers) and the detective procedural Magnum, P.I. (1988, CBS, 50.7 million viewers in the television history).