Professor Layton will return on the 3DS in 2013, as Level-5 announced a new portable entry in the series for Japan this morning during a Nintendo Direct presentation. Andriasang notes the game will be called "Professor Layton Choubunmei to A no Isan," and no information is available regarding a release in the United States, Europe, or other territories.
Level-5 CEO Akihiro Hino was on hand to reveal the game, teasing that it will be Layton's "last adventure." It isn't clear if Level-5 means to do away with Layton, or simply replace him as the series' main character for future games.
The next entry in the Professor Layton series is Professor Layton and the Miracle Mask for the 3DS. That game is due out in October and has players attempting to solve a mystery surrounding the nefarious Masked Gentleman.