When CBS introduced Gunsmoke on television on September 10, 1955, people knew the characters and stories played well on radio; the audio adventures had been airing for the past three years and would continue until 1961. Few suspected the television adaptation of the Dodge City, Kansas characters of the Old West would be so popular as to propel the show toward a longevity record.
The episode entitled “Matt Gets It” was the first of 635 episodes that would air over the next twenty years. When the final episode, “The Sharecroppers,” was broadcast on March 31, 1975, it capped off a record-breaking tenure that would not be rivaled until 2010, when Law and Order likewise wrapped up a 20-year run. While both series lasted for twenty years, Gunsmoke saw 179 more episodes than Law and Order.
UPDATE: On April 29, 2018, The Simpsons aired its 636th episode, surpassing Gunsmoke‘s record.