As far as MLB goes that would be the 1997 Seattle Mariners with 264.
Barry Bonds holds the record for career home runs with 762 and the mark for most homers in a season with 73.
Coors field
As of June 2014 Barry Bonds holds the record for most regular season homeruns. The record is 73 which beat Mark McGwire's record.
David Ortiz set the single-season record for most home runs by a Boston Red Sox player in 2006. He hit 54 home runs that year, which was the most in the American League.
Nobody has hit 400 home runs in a single season in Major League Baseball history. The record for most home runs in a season is 74, set by Barry Bonds in 2001.
Dave Klingman holds the record for most home runs hit during a retirement season. He hit 35 home runs in his 1987 final season.
Mark McGwire had over 70 home runs in one season
Dave Klingman holds the record for most home runs hit during a retirement season. He hit 35 home runs in his 1987 final season.
Barry Bonds holds the record for career home runs with 762 and the mark for most homers in a season with 73.
He holds the major league records for most home runs in a career (762) and most home runs in a season (73).
He holds the world record for the most home runs in a single season.
Coors field
As of June 2014 Barry Bonds holds the record for most regular season homeruns. The record is 73 which beat Mark McGwire's record.
David Ortiz set the single-season record for most home runs by a Boston Red Sox player in 2006. He hit 54 home runs that year, which was the most in the American League.
Nobody has hit 400 home runs in a single season in Major League Baseball history. The record for most home runs in a season is 74, set by Barry Bonds in 2001.
In MLB through the 2008 season, the record for home runs by a team in one season is 264 by the 1997 Seattle Mariners.
The record is still held by Barry Bonds.