Johnson officially signed a six-year deal with Atlanta that will pay the four-time All-Star an average of more than $20 million a year.
The deal is for $123.7 million, according to Johnson's agent, Arn Tellem.
Other teams could only offer Johnson five years and about $25 million less than the Hawks.
Johnson and the Hawks agreed to the maximum contract on Monday. Thursday was the first day free agents could sign contracts.
"Although I explored several different opportunities this offseason, Atlanta was the place I wanted to be," Johnson said in a statement released by the team.
BULLS: Chicago signed forward Carlos Boozer away from the Utah Jazz, giving the Bulls a two-time All-Star and the dominant big man they've craved for years.
Boozer agreed Wednesday to the deal, which several outlets reported is worth roughly $75 million over five years. The team did not disclose terms.
"I feel we have the talent here to begin competing for a title and I cannot wait to get started," Boozer said.
Celtics: General manager Danny Ainge confirmed the team has agreements in place with Paul Pierce and Ray Allen that would keep Boston's new Big Three intact for a run at a third NBA Finals in four years.
Ainge also said he expects to sign free agent center Jermaine O'Neal to fill in while center Kendrick Perkins recovers from knee surgery.
MAVERICKS: Brendan Haywood is coming back to Dallas.
Haywood agreed to a $55 million, six-year contract, according to a person familiar with negotiations.