Cztery.
http://torchlight.wikia.com/wiki/Torchlight_II
Torchlight II is divided into four major acts, each featuring a hub town and large overland areas as well as dungeons.
Act I: The Estherian Steppes, a mountainous region inhabited by the Estherians. The area's town is the Estherian Enclave.
Act II: The Mana Wastes, a desert which is home to the Zeraphi, their city Zeryphesh, and their enemies the Ezrohir.
Act III: Grunnheim, a haunted forest that contains the ruins of an ancient dwarven civilization. An Imperial Camp serves as the player's town.
Act IV: The Broken Mines, a short act that serves as the game's finale. The act's town is Minehead.
