Transylvania is a historical region located in Romania. The area popularly became associated with vampires after the publication of Bram Stoker's Dracula novel in 1897. As such, it has been named as the original homeland of Count von Count.
On Sesame Street, it is suggested that Transylvania is just as celebratory of numbers as the Count. Episode 2301 takes place on the national holiday Transylvania Counting Day, where citizens don snappy (and water resistant) jackets and hats to count to 40 with. In Episode 3262, it is shown that the nation's clocks don't operate on a normal 12-hour schedule, but rather a 19-hour one.
Though often merely referred to, Transylvania has been seen on the show on a few occasions. Episode 3012 contains a flashback to the day the Count, as a young lad, intends to leave his home for America. An edition of The Count's Storybook Theatre, "The Magnificent 7," takes place in a Transylvanian village.
In the examples above, it is shown that the residents of Transylvania speak English, but like the Count, they all pronounce their "V"s as "W"s, and vice-versa. Despite this, they seem also have their own regional language as well. The Count teaches Maria to count in Transylvanian in Episode 1130, and he also counted backwards in his native tongue to launch his rocket ship.
Like much of our world, a Grouch equivalent seems to exist as well, named Trashsylvania (mentioned as the home of Grundgetta's aunt in Episode 2730). Elsewhere, the location has been mentioned as being the homeland of The Muppet Show's wardrobe mistress Hilda, introducing a sketch taking place there in episode 119.