The population of Twin Peaks was originally only supposed to be 5,120. However, there was a backlash against rural-themed shows at the time, as networks were fearful that the burgeoning urban and suburban population of America would not be able to sympathize with shows set in small farming or industrial towns, so ABC requested that the sign read 51,201. In a "Visitor's Guide to Twin Peaks" tie-in book authorized by creators David Lynch and Mark Frost, a note tells readers that the population was indeed 5,120, but that the sign had a "typo."
The character of Madeleine Ferguson (Laura Palmer's lookalike cousin, played by the same actress) was created because David Lynch was so impressed by Sheryl Lee that he wanted to have her on the series full-time.
In the 2014 book Reflections: An Oral History of Twin Peaks by Brad Dukes, Jules Haimovitz (who was the president and COO of Spelling Entertainment while Twin Peaks was on) says that during the show's run, he got a call from the financier Carl Lindler demanding to know who killed Laura Palmer. Lindler told Haimovitz that he was asking not for himself but for then-president of the United States George Bush, who was in turn asking for Mikhail Gorbachev, then the leader of the U.S.S.R.
In Germany, broadcasting network RTL canceled the show after 20 episodes due to bad ratings because rival network SAT1 told the audience the identity of Laura's murderer before the first episode aired.
Steven Spielberg, who was a big fan of the show, was originally set to direct the first episode of the second season before David Lynch decided to direct it himself.
David Lynch: [Sunset Blvd] Lynch himself plays the character Gordon Cole who was named after a minor character (and real Paramount Studios employee) in Boulevard der Dämmerung (1950), a film Lynch has acknowledged as a major influence in his filmography, most notably in the similarly named Mulholland Drive (2001).