As reported today on the Disney Parks Blog

As many of you know, we’re in the midst of the largest expansion in Magic Kingdom history, which will nearly double the size of Fantasyland. In order to make way for this transformation, it’s important to let you know Mickey’s Toontown Fair will close in early February.

That doesn’t mean we’ve forgotten about some of your favorite characters. Mickey Mouse, Minnie Mouse and the Disney princesses will move to Town Square in the location currently known as Town Square Exposition Hall in spring 2011. Until that location is ready, they will continue to greet guests throughout Magic Kingdom. Meanwhile, Tinker Bell will relocate to Disney’s Hollywood Studios and her other fairy friends will appear later in the spring at Epcot. The Walt Disney World Railroad will stay open, but the Toontown station will remain closed during construction.
We hope you will pardon our dust as work progresses and if you’d like to experience Mickey’s Toontown Fair, you’ll have until Feb. 11 to make those plans. Remember, there are still many other entertainment experiences throughout Magic Kingdom to delight everyone in the family.
Fantasyland construction will be completed in phases with most new experiences open by 2013. This expansion is particularly exciting because it will enable us to share treasured stories with you in a whole new way. We’ll share more with you here as our work progresses.