Famed director Spike Lee organized the massive dance party for what would have been the star's 51st birthday.
"Fifty-one years ago, he was born into the world," said Lee, who directed the "They Don't Care About Us" music video for Jackson in 1996.
"I'm like everybody else - somebody who loved his talent," he said. "We're here to celebrate Michael Jackson."
Indeed, the birthday party had a celebratory tone - a welcome change from weeks of grieving Jackson's death.
He died just over two months ago of cardiac arrest after his doctor, Conrad Murray, gave him a lethal drug cocktail at his rented Bel Air estate in June.
The death was ruled a homicide last week.
Several thousand dancers packed themselves close together on the muddy Prospect Park grass facing a huge stage. Deejays played Jackson's music spanning his whole career - from his childhood with the Jackson Five to his final tracks.
There was a giant white birthday cake that read "Happy Birthday Michael Jackson" in red frosting. Balloons dotted the sky.
The biggest cheers came late in the day when the deejay played one of Jackson's best known hits, "Beat It."
"I've been into Michael Jackson since I was 1 year old," said Tariq Shade, 39, of Crown Heights, who wore a silver sequin glove on one hand. "I've always, always celebrated his birthday."
"I don't even remember life without him," actor Tracy Morgan said at Saturday's party. "Michael Jackson was everything."
"Happy birthday, Michael!" yelled Purcell Nurse, 28, of Crown Heights. "I wasn't able to go to one of his concerts, but I'll always remember this concert."
Brooklyn Borough President Marty Markowitz took the stage to declare Aug. 29 "Michael 'King of Pop' Jackson Memorial Day" in Brooklyn.
"We all know Michael Jackson had fans around the world, but nowhere more than Brooklyn," Markowitz said.
Brooklyn City Councilwoman Letitia James last week suggested adding "Jackson" to the Hoyt-Schermerhorn subway station's name. The station served as an iconic backdrop for the 1987 music video of "Bad."
Meilan Gee, 59, flew all the way from Los Angeles to attend the birthday party.
"I had to be here today," she said. "I went to Neverland, his house, his mother's house. I have to be wherever he is."
Timbe Crump, 38, came from Milwaukee for the weekend and didn't want to miss the bash.
"We planned the trip around this," she said. "It's a day to celebrate his life and his accomplishments."