The popular conservationist and TV personality died in September 2006 after he was pierced in the heart by a stingray.
Many of those who went to the zoo for the day dressed in Irwin's trademark khaki clothes, The Daily Telegraph reported Thursday.
"The response worldwide has just been tremendous," said Terri Irwin, the adventurer's widow -- and the mother of his two young children, who were present at the event and helped unveil a bronze rendering of their family at the site where the zoo began in 1970.
"I think that what happened to Steve was such a tragedy, but it's given everyone the opportunity to take stock and re-evaluate what's truly important, and that has to be family and our wildlife. I think Steve would've been very proud, but I know he would've said, 'It's about me crocs, mate, not about me.'"
Terri Irwin just published "My Steve," a book about her life with the famed adventurer.
"I think we fell desperately in love at first sight and it's kind of our journey through life together," she said.