Gunsmoke is an American television Western drama series created by director Norman MacDonnell and writer John Meston. The stories take place in and around Dodge City, Kansas, during the settlement of the American West. The television version ran for 20 seasons from September 10, 1955 to March 31, 1975 on CBS with 635 total episodes, and it is currently tied with Law & Order as the longest running primetime drama in U.S. television history. In 2009, the half-hour animated series The Simpsons entered its 21st season, becoming the first show to surpass it in longevity.
Gunsmoke was TV's No. 1 ranked show from 1957 to 1961 before slipping into a decline after expanding to an hour. In 1967, the show's 12th season, CBS planned to cancel the series, but widespread viewer reaction (including a mention in Congress and pressure from the wife of the head of programming at CBS) prevented its demise. The show continued on in a different time slot: early evening on Mondays instead of Saturday nights. This seemingly minor change led to a spike in ratings that saw the series once again reach the top 10 in the Nielsen ratings until the 1973–1974 television season. In September 1975, the show was canceled after a twenty-year run. 30 TV Westerns came and went during its 20-year tenure, and Gunsmoke was the only Western still airing when it was canceled.