1. The show was almost called 123 Avenue B, but it was changed due to the fact that it was a real New York City address.
2. "Sing a Song" was originally intended to be the show's opening theme song. The Carpenters later released a cover of the song.
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3. Cookie Monster predates the show by 3 years. Jim Henson originally designed an early version of the character in 1966, for a cracker commercial.
4. Roosevelt Franklin was one of the first breakthrough characters on the show. However, his character was dropped after season 7 following letters complaining of the character was a negative African-American stereotype.
5. The first Mr. Snuffleupagus design had a much more freighting and awkward appearance. His look was softened shortly after his initial appearance.
6. The rumor that Bert and Ernie are gay dates back to 1980, when Kurt Andersen questioned the duo’s sexuality in his book The Real Thing. For the record, they are not gay.
7. The Count's birthday is October 9, 1,830,653 B.C.
8. Originally the Muppets and humans were not intended to interact. However, this changed once producers learned that the audiences were focusing their attention on the Muppets and ignoring the actors.
9. In 1970, Ernie’s signature song "Rubber Duckie" reached No. 16 on the Billboard Hot 100.
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10. Big Bird's height is 8'2."
11. Ernie wears horizontal stripes on his sweater to make him appear more relaxed; while Bert wears vertical stripes on his sweater to make him appear more uptight.
12. Oscar the Grouch was originally orange.
13. In 1990, after Jim Henson’s untimely death, Kermit the Frog disappeared from the show. He reappeared in new segments in 1998.
14. In 1980, C-3PO and R2-D2 visited Sesame Street.
15. Guy Smiley’s real name is Bernie Liederkrantz.
16. Originally Snuffleupagus was only be seen by Big Bird. The adults on the show refused to believe he existed and thought he was just Big Bird’s imaginary friend.
17. Big Bird's teddy bear is named Radar, a nod to the character on MASH who always slept with a teddy bear.
18. In 1992, an episode was produced were Snuffy’s parents get a divorce. The episode never aired, it did not test well with children.
19. Kevin Clash, who used to voice Elmo, also voiced Baby Sinclair on Dinosaurs.
20. James Earl Jones was the first ever guest star, he recited the alphabet.
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21. Sesame Street is the longest running children’s program in the U.S. In 2008, it was estimated that 77 million Americans had watched the series as children.
Facts via: IMDb and Muppet Wiki