The infamous co-founder of the Black Mafia Family crime enterprise is out from behind bars ... and now he's finishing his sentence in comfier surroundings in Florida.

The Federal Bureau of Prisons tells TMZ ... Demetrius "Big Meech" Flenory was transferred Tuesday from FCI Coleman Low in Wildwood to community confinement overseen by the BOP's Miami Residential Reentry Management Office.

Our sources say Big Meech is now serving his sentence in a halfway house.

Big Meech was arrested in 2005, and in 2008 he was sentenced to 30 years in prison after being convicted on charges related to drug trafficking and money laundering. Earlier this year a judge shortened his sentence by almost 3 years.

It's unclear when Big Meech will officially finish his sentence ... but the big thing here is he's no longer in federal prison.

Brittany K. Barnett, attorney for Big Meech and co-founder of the Buried Alive Project, tells TMZ ... she's "overjoyed" Flenory is free after nearly 20 years behind bars, and that he used his time in prison to focus on his own personal growth, and he has the opportunity now to start a new chapter in his life.

Meanwhile, 50 Cent has been the frontrunner in keeping the BMF story alive ... delivering a successful docuseries and a TV series -- even turning Meech's son, Lil Meech, into a legit actor.

Hip Hop has rallied around "BMF" for years ... Snoop Dogg, 2 Chainz, Lil Baby, Yung Miami and even Eminem have guest-starred in the series, which now stands at 3 seasons.

It will be interesting to see if Big Meech gets out in time for the upcoming fourth series, which has already been greenlit.