Sesame Street character debuts

The following is a list of known sources for when certain Sesame Street characters made their debut on the show.

Season 1

 * Big Bird - Debuted in the premiere episode.
 * Oscar the Grouch - Debuted in the very first episode.
 * Ernie and Bert - Appeared in the first episode, having previously appeared in the first test pilot.
 * Kermit the Frog - Appears in the first episode, having already been around since Sam and Friends in 1955.
 * Cookie Monster - Appears in the first episode.
 * Beautiful Day Monster - Appears in segments known to have debuted during the first season; He previously appeared in an Ed Sullivan sketch Happy Girl Meets a Monster, which aired six months before Sesame Street premiered.
 * Grover - Appears in segments known to have debuted during the first season.
 * Professor Hastings - appears in segments known to have debuted in the first season.
 * Lefty the Salesman - Appears in segments known to have debuted in the first season.
 * Roosevelt Franklin and his mother - Appear in segments known to have premiered in the first season.
 * Little Bird - appears in segments known to have premiered during the first season.
 * Guy Smiley - First appears, unnamed, in an insert in Episode 0010.
 * Betty Lou - Appears in segments known to have premiered in the first season.
 * Bip Bippadotta

Season 2

 * Sherlock Hemlock - A Time Magazine article from 1970 mentions him as a new character in the second season. He made his debut in the second season premiere.
 * Herbert Birdsfoot - A Time Magazine article from 1970 mentions him as a new character in the second season.
 * Little Jerry and the Monotones - Their song "Mad" was listed as a Season 2 sketch in 40 Years of Sunny Days.
 * Herry Monster
 * Slimey
 * Prairie Dawn
 * Farley
 * Simon Soundman
 * Granny Fanny Nesselrode

Season 3

 * Mr. Snuffleupagus - Big Bird first meets him in the third season premiere. Songs from the Street and Sesame Street Unpaved also cite this as his debut season.
 * Harvey Kneeslapper
 * Mr. Johnson
 * The Amazing Mumford
 * The Martians
 * The Busby Twins

Season 4

 * Count von Count - Songs From the Street refers to this as The Count's debut season; He makes his debut in the season premiere.
 * Sam the Robot - Sam meets Susan and Gordon in the season premiere.
 * Frazzle
 * Baby Breeze
 * Same Sound Brown
 * Smart Tina
 * Suzetta Something

Season 5

 * Biff and Sully - Songs From the Street refers to this season as their first appearance.
 * Twiddlebugs - The main Twiddlebug family was introduced in this season, although the species was introduced in Season 2.
 * Fred the Wonder Horse
 * Gladys the Cow
 * Little Chrissy and the Alphabeats

Season 6

 * Rodeo Rosie - She meets the cast in the season premiere.
 * Don Music
 * Mr. Chatterly
 * Hard Head Henry Harris

Season 8

 * The Countess

Season 9

 * Two-Headed Monster
 * Brad

Season 10

 * Barkley - Created specially for the tenth season according to Imagination Illustrated: The Jim Henson Journal; Appears in the season premiere.
 * Telly Monster - Telly moves to the neighborhood in a season ten episode; 40 Years of Sunny Days lists a clip from this episode as being from that season.
 * Bruno the Trashman
 * Polly Darton

Season 11

 * Elmo - Sesame Street Unpaved, Sesame Street 35 Years Anniversary Game, and Imagination Illustrated: The Jim Henson Journal cite Elmo as making his debut in 1979, as a generic background monster; He was first called Elmo in season 12, according to a season 12 press kit.

Season 12

 * Forgetful Jones and Clementine - A season 12 press kit mentions them as new characters debuting in this season. Buster the Horse is also referred to as a new character, though the puppet had been around since at least 1974.
 * Warren Wolf - A season 12 press kit refers to him as debuting this year.
 * Honkers - A season 12 press kit refers to this as the debut season for the Honkers.
 * Ferlinghetti Donizetti - A season 12 press kit refers to him as a new character this season.
 * Deena and Pearl - A season 12 press kit refers to this as their debut season.
 * Poco Loco - A season 12 press kit refers to this as his debut season, although he was on the show since at least 1974.
 * Dr. Nobel Price - A season 12 press kit refers to this as his debut season.
 * Masha - A season 12 press kit refers to this as her debut season.
 * Grundgetta

Season 13

 * Aristotle - Sesame Street: A Celebration - 40 Years of Life on the Street page 57 says that he debuted that year.

Season 15

 * Irvine

Season 16

 * How Now Brown and the Moo Wave

Season 17

 * Leo the Party Monster
 * Ernestine
 * Hoots the Owl
 * The Oinker Sisters

Season 18

 * Baby Natasha
 * Placido Flamingo
 * Shelley the Turtle
 * Chip and Dip
 * Flo Bear
 * Juliet
 * Athena

Season 19

 * Alice Snuffleupagus - Songs From The Street cites 1987 as the year of her debut.
 * Ruby

Season 21

 * Wolfgang the Seal
 * Preston Rabbit
 * Vincent Twice

Season 22

 * Humphrey
 * Stella

Season 23

 * Rosita - Debuted in Episode 2888. Songs From the Street also cites 1991 as her debut year.
 * Baby Bear - Debuted in Episode 2909.
 * Joey and Davey Monkey - Appeared as early as Episode 2953. Sesame Street: A Celebration - 40 Years of Life on the Street, page 132, incorrectly cites Season 24 as their debut season.
 * Benny Rabbit
 * Roxie Marie
 * Merry Monster
 * Baby Tooth and the Funky Funk
 * Chicago
 * Monty
 * Colambo
 * Goldilocks

Season 24

 * Kingston Livingston III - first appears in Episode 3103
 * Stinky the Stinkweed - appears in Episode 3133 in the story "The Stinkweed and the Sun."
 * Cyranose de Bergerac
 * Horatio the Elephant
 * Wanda Cousteau

Season 25

 * Zoe - Songs from the Street cites 1993 as Zoe's debut.
 * Sherry Netherland
 * Ingrid
 * The Squirrelles

Season 29

 * Elizabeth

Season 31

 * Lulu
 * Little Murray Sparkles

Season 32

 * Groogel/Phoebe
 * Mel
 * Mooba/Googel
 * Narf

Season 34

 * Curly Bear - She was born in Episode 4055.

Season 36

 * Murray Monster - debuts as a nameless monster interviewing kids. He would later get a name during Season 38.

Season 37

 * Abby Cadabby - She moves to Sesame Street in the season premiere, after appearing on The Today Show just a few hours earlier.
 * Mrs. Crustworthy

Season 39

 * Ovejita

Season 41

 * Segi

Season 47

 * Julia - While the character first appeared in 2015, her Muppet form appears on the show in Episode 4715.
 * Rudy