Fillydelphia

Filly Delphia, frequently spelled Fillydelphia and rarely spelled Phillydelphia, is a city in Equestria that is populated by both ponies and dragons.

Development
Ponyville "was originally Fillydelphia..." Lauren Faust "wanted Ponyville to be Fillydelphia originally. Obviously that didn't pan out, but [she] was glad [they] got to use the name somewhere else."

Fillydelphia's Dragon Town and its dragons were "closely vetted by the show in the script and art, and as a result some things were changed to bring it closer into line for what the show wants to do." The IDW comics "got some direction on how the Dragon part of town should look." Artist design choice and what is explored in the TV show were combined.

Season one
In Swarm of the Century, the town of Fillydelphia is mentioned.

Season two
In A Friend in Deed, Fillydelphia is mentioned. In It's About Time, Fillydelphia is mentioned. In Hurricane Fluttershy, Fillydelphia is mentioned.

Season three
In Apple Family Reunion, Fillydelphia is mentioned. In Games Ponies Play, the city of Fillydelphia is mentioned.

Season four
In Pinkie Pride, it is shown. In Testing Testing 1, 2, 3, Fillydelphia is mentioned. In Inspiration Manifestation, Fillydelphia is mentioned. In Twilight's Kingdom - Part 2, it is shown.

Software
In Gameloft's mobile game, Fillydelphia has been listed.

In Discovery Family (previously the Hub Network)'s online game Equestrivia Challenge, Fillydelphia has been offered as an incorrect answer to multiple questions.

IDW comics
In My Little Pony: Friends Forever, Fillydelphia is mentioned in Friends Forever Issue 13 and is featured in Friends Forever Issue 14.

Merchandise and promotional material
Filly Delphia/Phillydelphia/Fillydelphia is included by various merchandise.

Fillydelphia is mentioned in a Hub advertisement and is listed in a Discovery Family (previously Hub) Facebook question.