The most recent data is:
•Approximately 61 percent (1,189,709) of all separated OEF/OIF/OND Veterans have used VA health care since October 1, 2001.
•Between April 1, 2014 and March 31, 2015, a total of 723,143 of these Veterans accessed VA health care.
•The frequency and percent of the three most common diagnoses were: musculoskeletal ailments (735,582 or 61.8 percent); symptoms, signs, and ill-defined conditions (conditions that do not have an immediately obvious cause or isolated laboratory test abnormalities) (690,869 or 58.1 percent); and mental disorders (685,540 or 57.6 percent). A Veteran can have more than one diagnosis.
Abbreviations: Operation Enduring Freedom (OEF), Iraqi Freedom (OIF), and New Dawn (OND)
These statics do not include Desert Shield and Desert Storm.
The older reports are also available at the linked site. The 900,000 number was correct at the time, but it is only OEF/OIF/OND veterans, not other Iraq veterans, and it includes any who used VA health care. It doesn't mean they were necessarily injured in a war.