A Blackstone man pleaded guilty to stealing dozens of identities and using them in forged prescriptions at pharmacies across the state, Attorney General Martha Coakley’s office said Thursday. John Tropea, 59, pleaded guilty Wednesday in Suffolk Superior Court to 76 charges of identity fraud, 76 charges of obtaining drugs by fraud, 40 counts of making false health care claims, and conspiracy. Tropea was sentenced to 2½ years in jail with five years of probation. Prosecutors said Keith Huguenin, 33, of Woonsocket, R.I., helped Tropea write prescriptions using a doctor’s pad Tropea had stolen. Tropea would then go to various pharmacies to obtain drugs such as hydrocodone, Coakley’s office said. Tropea conspired with Huguenin to steal the identities of other people in six counties in 2009, the attorney general’s office said. In April, Huguenin pleaded guilty to three counts each of identity fraud, obtaining drugs by fraud, and filing false health care claims, and one count of conspiracy. Huguenin was sentenced to three years of probation with continued drug treatment, Coakley’s office said.Sarah N. Mattero can be reached at email@example.com.