Witnesses saw Anthony, who had been acquitted on July 5 of culpability in Caylee's death, exit escorted by guards wearing bullet-proof vests and carrying rifles, and stepped into a black SUV a few minutes after midnight. The Orange County Jail later confirmed her release.
A crowd of 300 had been waiting since midafternoon Saturday for Anthony's release, and many rushed into the street to follow the vehicle as she was driven away, briefly blocking the eastbound lanes of a six-lane road before police cleared them away.
Many carried signs for and against Casey Anthony, and some chanted Caylee's name.
A large police presence included the sheriff's mobile command center, five horse-mounted officers and at least 20 uniformed officers on foot, many wearing bullet-proof vests. Three news helicopters hovered overhead.
Since her acquittal, Anthony's future after three years in jail has been the subject of much speculation, but with no publicly known facts beyond her jail departure date.
Pool reporters inside the jail saw Anthony and her attorney Jose Baez whiz by them in the lobby and exit swiftly through the front door.
"She was just tunnel vision on that door," said Tony Zumbado, an NBC News cameraman. Anthony's only words were "Thank you" to a jail sergeant, he said.
A second pool reporter, Matt Sedensky of the Associated Press, quoted jail officials as saying Anthony -- wearing the tight hair bun seen during her trial, a bright pink shirt, jeans and bright blue sneakers -- left with the $537.68 remaining in her inmate account.
CROWD WAITING
Lori Richards, 54, of Daytona Beach and three friends set up a tent at 3 p.m (1900 GMT) outside the jail where they huddled through a brief lightning storm.
"We're here to support Caylee and we want them (the public) to boycott anything Casey or any of the Anthonys do," Richards said.
Anthony's release had been planned with the same precision that marked her high-profile murder trial.
In recognition of the massive coverage expected of the release, media representatives and jail managers negotiated a plan which, much like modern war coverage, allowed embedded pool reporters and photographers to document her departure.
Anthony's trial revealed gruesome details of Caylee's death and the disposal of the toddler's remains in trash bags in swampy woods. The trial brought out evidence of Casey Anthony relishing her life, partying and shopping, after Caylee died.
Casey Anthony's parents and brother had testified at the widely telecast trial. Her lawyer Baez acknowledged her outward lack of emotion over the death was "bizarre."
Her acquittal was met with shock and derision by much of the public, egged on by outraged television commentary.
Charles Greene, Anthony's defense lawyer in a related civil defamation lawsuit, told a judge on Friday that he had received seven threats against her.