June 2006 – Los Angeles County
Welfare recipients and their friends and relatives defrauded taxpayers of $500 million a year through the county's child care programs, a grand jury report concluded. The report found that nearly half the $1.1 billion CalWORKS child care program is lost to fraud. DPSS staff said the grand jury study shouldn't be used to draw conclusions about child-care fraud because it was not specifically a fraud study.
April 2007 – Los Angeles County
Through their citizen children, illegal immigrants in Los Angeles County collect $420 million annually in welfare and food stamps, according to a report requested by 5th District County Supervisor Michael D. Antonovich. The Los Angeles County Department of Public Social Services told the supervisor that payments to illegal immigrants' children amount to approximately 24% of the county's combined CalWORKS and food stamps budget. According to Antonovich's office, illegal immigrants annually cost the county $360 million in health care and $220 million in incarceration costs.
May 2007 – Los Angeles County
While exact figures are difficult to tally, experts estimate as much as $300 billion a year is lost to health care fraud in the United States - more than half of it to organized crime. Medi-Cal spends about $34 billion annually to provide care for about 7 million indigent Californians - with about $3 billion of that lost to fraud, experts say. The state Attorney General's Office has a bureau that deals specifically with Medi-Cal fraud. It's prosecuted about 1,000 such cases over the past eight years - double the number for the previous eight years. Most, officials say, are related to organized crime.
these are from California's Department of Social Services. I have run now, i can't use my google fu, but i'm sure other states have similar stats.
http://www.dss.cahwnet.gov/fraud/PG270.htm