Level 21 is the first content update for The Simpsons: Tapped Out. It was released on September 21, 2012, and came nearly a month after the game's re-launch on the App Store.
Level 21 was introduced, a long-awaited level for players who had finished Level 20 months before. The Muntz House was unlocked with Level 21, and unlocked Nelson. Springfield Library was added as a Level 12 building, and unlocked Martin when built.