Horton (voice)
Mayor (voice)
Kangaroo (voice)
Vlad (voice)
Morton (voice)
Councilman / Yummo Wickersham (voice)
Dr. Mary Lou Larue (voice)
Tommy (voice)
Sally O'Malley (voice)
Mrs. Quilligan (voice)
Narrator (voice)
Rudy (voice)
Miss Yelp (voice)
JoJo (voice)
Hedy / Hooly (voice)
Old Time Who (voice)
Helen (voice)
Heather (voice)
Town Cryer (voice)
Who (voice)
Another Who (voice)
Who Mom (voice)
Hildy / Holly (voice)
Who Kid (voice)
Wickersham Guard 1 (voice)
Willie Bear (voice)
Joe (voice)
Who Girl (voice)
Helga (voice)
Obnoxious Who (voice)
Katie (voice)
Heidi / Haley (voice)
Hanna (voice)
Glummox Mom (voice)
Wickersham Guard 2 (voice)
Angela (voice)
Jessica (voice)
The Dentist (voice)
Who Child #1 (voice)
Additional Voices (voice)
Additional Voice (voice)
Jojo (singing voice) (uncredited)