Horton

Jim Carrey Horton (voice) Steve Carell Mayor (voice) Carol Burnett Kangaroo (voice) Will Arnett Vlad (voice) Seth Rogen Morton (voice) Dan Fogler Councilman / Yummo Wickersham (voice) Isla Fisher Dr. Mary Lou Larue (voice) Jonah Hill Tommy (voice) Amy Poehler Sally O'Malley (voice) Jaime Pressly Mrs. Quilligan (voice) Charles Osgood Narrator (voice) Josh Flitter Rudy (voice) Niecy Nash Miss Yelp (voice) Jesse McCartney JoJo (voice) Shelby Adamowsky Hedy / Hooly (voice) Jack Angel Old Time Who (voice) Caitlin Rose Anderson Helen (voice) Emily Anderson Heather (voice) Jan Rabson Town Cryer (voice) John Cygan Who (voice) Jess Harnell Another Who (voice) Debi Derryberry Who Mom (voice) Samantha Droke Hildy / Holly (voice) Karen Disher Who Kid (voice) Marshall Efron Wickersham Guard 1 (voice) Bill Farmer Willie Bear (voice) Jason Fricchione Joe (voice) Heather Goldenhersh Who Girl (voice) Selena Gomez Helga (voice) Jimmy Hayward Obnoxious Who (voice) Joey King Katie (voice) Christina Martino Heidi / Haley (voice) Ellie Martino Hanna (voice) Laraine Newman Glummox Mom (voice) Tim Nordquist Wickersham Guard 2 (voice) Colleen O'Shaughnessey Angela (voice) Laura Ortiz Jessica (voice) Joe Pasquale The Dentist (voice) Connor Anderson Who Child #1 (voice) Isabella Acres Additional Voices (voice) Bob Bergen Additional Voices (voice) Jeff Biancalana Additional Voices (voice) Madison Davenport Additional Voices (voice) Teresa Ganzel Additional Voices (voice) Kathy Graves Toon Additional Voice (voice) Sherry Lynn Additional Voices (voice) Danny Mann Additional Voices (voice) Mona Marshall Additional Voices (voice) Mickie McGowan Additional Voices (voice) Madison Pettis Additional Voices (voice) Grace Rolek Additional Voices (voice) Jennessa Rose Additional Voices (voice) Ariel Winter Additional Voices (voice) Fletcher Sheridan Jojo (singing voice) (uncredited)