Source of information: 2001 Annual Report on Osteopathic Medical Education, page 14 (of 64)
Total number of osteopathic physicians, AND total number of active osteopathic physicians - breakdown by states
http://www.aacom.org/data/annualreport/annualreport2001.pdf
WARNING: Total size is 4.9 MB
Data accurate as of June 1, 2001
Quick review of data
Pennsylvania - Total (5289), Active (4688)
New York - Total (2823), Active (2647)
Michigan - Total (5115), Active (4346)
Ohio - Total (3473), Active (3071)
Florida - Total (3336), Active (2689)
California - Total (2380), Active (2244)
Texas - Total (2958), Active (4688)
Those are the top states. If you want to check an individual state, it's in the annual report (quite interesting, also shows # of applicants for each school)