Unlike many other parks it is open 24 hours a day, with security guards in attendance when park keepers go home.
Director of park operations at the London Legacy Development Corporation, which runs the park, Mark Camley said: "The park is proving really popular with local people bringing their kids out, all summer kids have been loving it.
"We were slightly worried when we opened South Park that it would take visitors from North Park but visitor numbers to both have been really good - it seems to be going from strength to strength."
The park is able to count the number of visitors because of light sensors built into the design.
One of the three million was plantsman and garden designer Piet Ouldof, whose planting designs have been integral to the South Park. He visited earlier this month to inspect progress.
"He was really pleased with how it was looking," Camley said.
Next week the park will welcome back some of its original stars for Paralympic Day. London 2012 medallists and others will compete again alongside the Liberty Festival which features deaf and disabled artists bring an exciting line-up.
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