All three were killed by car collisions in Collier County, documents released by Public Employees for Environmental Responsibility said.
One was a mature radio-collared female, another was a juvenile un-collared female and the third was a year-old un-collared male, the PEER documents said.
The group said 2012 could become deadliest on record, threatening to exceed the record 24 panther deaths that occurred in 2011.
Panther deaths are likely exceeding replacement from new litters, it said, and the loss of females, especially of reproductive age, is harder for a small population to bear.
The exact number of Florida panthers remaining in the wild is not known but most estimates range between 100 and 120 animals.
Undisturbed wild habitat for the Florida panther continues to shrink from sprawling developments, PEER said.
"Despite all the scientific conferences and papers, our Florida panther management strategy basically is to collect the carcasses and hope for the best," said Jeff Ruch, Executive Director of PEER, which is litigating for protected panther habitat.
"Rising road-kill is not a good sign for the Florida panther."