The following is a list of known sources and Earliest Known Appearances for when Sesame Street characters made their debut on the show.
Season 1 (1969-1970)
- Big Bird and Oscar the Grouch — Appear in the premiere episode.
- Ernie and Bert — Appear in the first episode, having previously appeared in the pilot episodes.
- Kermit the Frog — Appears in the first episode, having already been around since Sam and Friends in 1955, as well as the fourth test show.
- Cookie Monster — Appears in the first episode, having previously appeared in the fourth test show.
- Gordon, Susan, Bob and Mr. Hooper — Cast regulars appear in the first episode, having previously appeared in the pilot episodes.
- Buddy and Jim — Appear in the first episode, having previously appeared in the pilot episodes.
- Jennie — Appears in the first episode.
- Granny Bird — First appears in Episode 0030 as the Big Bird puppet with a flowered hat, shawl, glasses and purse. Converses with Big Bird off screen.
- Grover — a prototype for Grover appeared as part of Jim Henson's Muppet act in early variety show appearances in the 1960s. The character gained the name Grover in Episode 0125, and his appearance and mannerisms would be refined by the second season (see: Grover#Origins).
- Beautiful Day Monster — Appears in segments known to have debuted during the first season; He previously appeared in the Ed Sullivan Show sketch "Happy Girl Meets a Monster", which aired six months before Sesame Street premiered.
- Professor Hastings — (EKA: Episode 0096)
- Lefty the Salesman — (EKA: Episode 0079)
- Roosevelt Franklin — (EKA: Episode 0068)
- Little Bird — (EKA: Episode 0028)
- Guy Smiley — First appears, unnamed, in an insert in Episode 0010.
- Bip Bippadotta — First appears in Episode 0014 singing "Mahna Mahna with two Anything Muppets.
Season 2 (1970-1971)
- Betty Lou — (EKA: Episode 0138)
- Prairie Dawn — (EKA: Episode 0252)
- 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. He first appears in Episode 0132.
- Little Jerry and the Monotones — Their song "Mad" was listed as a Season 2 sketch in 40 Years of Sunny Days.
- Herry Monster — (EKA: Episode 0131)
- Slimey — First appears and introduced in Episode 0202.
- Farley — (EKA: Episode 0131)
- Simon Soundman — (EKA: Episode 0170)
- Granny Fanny Nesselrode — (EKA: Episode 0199)
- Miguel — (EKA: Episode 0179)
- Tom — (EKA: Episode 0246)
- Larry and Phyllis — They first appear in the premiere, Episode 0131.
- David — (EKA: Episode 0268)
- Willy
Season 3 (1971-1972)
- Mr. Snuffleupagus — Big Bird first meets Snuffy in the third season premiere. Songs from the Street and Sesame Street Unpaved also cite this as his debut season.
- Maria, Luis, Molly and Rafael — Cast regulars appear in the season premiere, Episode 0276.
- Linda — Episode 0326
- Harvey Kneeslapper
- Mr. Johnson — (EKA: Episode 0276)
- The Amazing Mumford
- The Martians
- The Busby Twins
- Antonio
- Wally and Ralph
- Mr. Macintosh
Season 4 (1972-1973)
- 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
- Kate
Season 5 (1973-1974)
- 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 (1974-1975)
- Rodeo Rosie — She meets the cast in the season premiere.
- Don Music
- Mr. Chatterly
- Hard Head Henry Harris
Season 7 (1975-1976)
- Buffy — first appears in Episode 0802.
Season 8 (1976-1977)
- Olivia — first appears in Episode 0950; properly introduced in Episode 0957
- The Countess - first appears in Episode 0953.
Season 9 (1977-1978)
Season 10 (1978-1979)
- 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 Episode 1257.
- Bruno the Trashman — (EKA: Episode 1564)
- Polly Darton
Season 11 (1979-1980)
- 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.
- Grundgetta - Appeared as early as Episode 1443
- Deena — (EKA: Episode 1403)
- Pearl — (EKA: Episode 1441)
Season 12 (1980-1981)
- Forgetful Jones and Clementine — A season 12 press kit mentions them as new characters debuting in this season. They first appear in Episode 1446. 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.
- 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, appearing as early as Episode 1455
- Masha — Episode 1447
- Irvine - Appeared as early as Episode 1556
Season 13 (1981-1982)
- Aristotle — Sesame Street: A Celebration - 40 Years of Life on the Street page 57 notes that he debuted that year.
Season 16 (1984-1985)
Season 17 (1985-1986)
Season 18 (1986-1987)
- Gina — Episode 2253
- Baby Natasha
- Placido Flamingo
- Shelley the Turtle
- Chip and Dip
- Flo Bear - Episode 2277
- Juliet
- Athena
- Sonny Friendly
Season 19 (1987-1988)
Season 20 (1988-1989)
- Mike
- Hiroshi — Debuts in Episode 2459.
- Gabi — Episode 2615
Season 21 (1989-1990)
- Wolfgang the Seal - Episode 2618
- Preston Rabbit - Episode 2616
- Vincent Twice
- Mr. Handford — Debuts in Episode 2620.
- Lillian
- Savion
Season 22 (1990-1991)
- Benny Rabbit - Debuted in Episode 2811; introduced in Episode 2815.
- Humphrey - Debuted in Episode 2851
- Merry Monster - Debuted in Episode 2854
- Baby Bear and Goldilocks — Debuted in Episode 2866
- Chicago - Appears in Episode 2826 as a generic lion; earliest named appearance is Episode 2911
- The Grand High Triangle Lover and Norman - Debuted in Episode 2871
Season 23 (1991-1992)
- Rosita — first appeared in Episode 2887; introduced in Episode 2888.
- Joey and Davey Monkey — Appeared in Episode 2953. Sesame Street: A Celebration - 40 Years of Life on the Street page 132, incorrectly cites Season 24 as their debut season.
- Roxie Marie - Debuted in Episode 2910
- Baby Tooth and the Funky Funk - Debuted in Episode 2943
- Monty — Debuted in Episode 2939.
- Colambo
- Horatio the Elephant
- Cyranose de Bergerac
Season 24 (1992-1993)
- Kingston Livingston III — first appears in Episode 3103
- Stinky the Stinkweed — appears in Episode 3133 in the story "The Stinkweed and the Sun."
- Wanda Cousteau - first appears in Episode 3128
Season 25 (1993-1994)
- Zoe — Songs from the Street cites 1993 as Zoe's debut. She first appears in Episode 3136.
- Sherry Netherland — Episode 3136.
- Ingrid — Episode 3136.
- Ruthie — Episode 3136.
- Carlo — Episode 3136.
- Lexine - Episode 3139.
- Tarah — Episode 3136.
- Celina — Episode 3136.
- Angela and Jamal — Episode 3136.
- The Squirrelles - Episode 3156.
Season 29 (1997-1998)
- Elizabeth - first appears in Episode 3656
Season 30 (1998-1999)
Season 31 (2000)
- Lulu - first appears in Episode 3878
- Little Murray Sparkles - first appears in Episode 3852
Season 32 (2001)
Season 34 (2003)
- Curly Bear — She was born in Episode 4055.
Season 36 (2005)
- Murray Monster — debuts as a nameless monster interviewing kids. He would later get a name during Season 38.
Season 37 (2006)
- Abby Cadabby — She moves to Sesame Street in the season premiere, after appearing on The Today Show just a few hours earlier.
Season 38 (2007)
Season 39 (2008)
- Ovejita
- Leela — first appeared in Episode 4161; properly introduced in Episode 4164
Season 41 (2010)
Season 44 (2013-2014)
Season 46 (2016)
Season 47 (2017)
- Julia — While the character first appeared in 2015, her Muppet form debuts on the show in Episode 4715.