Here is a link to the SSI Annual Statistical Report, 2009. The report provides a wealth of statistical information on SSI.
http://www.ssa.gov/policy/docs/statcomps/ssi_asr/index.html/
Highlights :
Size and Scope of the Supplemental Security Income Program
* About 7.7 million people received federally administered payments in December 2009.
* The average monthly payment in December 2009 was $499.
* Total payments for the year were more than $46 billion, including almost $4 billion in federally administered state supplementation.
Profile of Recipients
* The majority were female (55 percent).
* Sixteen percent were under age 18, 58 percent were aged 18 to 64, and 26 percent were aged 65 or older.
* Most (85 percent) were eligible on the basis of a disability.
* Six out of 10 recipients under age 65 were diagnosed with a mental disorder.
* More than half (57 percent) had no income other than their SSI payment.
* Thirty-four percent of SSI recipients also received Social Security benefits.
* Of the people receiving SSI benefits, about 2 percent were residing in a Title XIX institution where Medicaid was paying more than half of the cost.
* Despite their disabilities, about 340,000 recipients (5.2 percent) were working in December 2009.