The 45-year-old won five championships in three weight classes, winning the WBA bantamweight title, the IBF and WBO junior bantamweight titles and the IBF featherweight belt.
Tapia's career also was marked by cocaine addiction, alcohol, depression and run-ins with the law. He was hospitalized for three days in 2007 after an apparent cocaine overdose.
Tapia last fought in June, defeating Mauricio Pastrana in an eight-round decision.
Police said Tapia's death doesn't appear to be suspicious.
The Associated Press contributed to this report.