Lee County Coroner Bill Harris said the three officers were shot around 11:30 p.m. on Sunday while on a "routine domestic call" at the trailer park in south Auburn.
"When the officers arrived they encountered gunfire," Harris said. "One was airlifted from the scene and he later died. The other two were transported. One is critical."
Auburn police dispatchers said that the gunman was still on the loose early Monday and the search was ongoing.
The Alabama state police issued a "Blue Alert," issued only in the death of a law enforcement officer, and it asked for help in catching a 29-year-old man last seen wearing body armor and a helmet.
No motive for the shooting was given.