The ark was built by Christians who said they believe the biblical story was a historical event.
Critics have said the attraction should not have received tax incentives as it contradicts science education.
The ark is based on a biblical story of a man who received an apocalyptic warning from God about a massive flood.
Answers in Genesis, the ministry that built the ark, said the ship's dimensions are based on those described in the Bible.
The ark is also 85ft (26m) wide and 51ft (15m) high, according to the group.
The ark, which is about 40 miles (64km) south of Cincinnati, Ohio, in Williamstown, features displays of animals in cages as well as exhibits on the group's theories on the world's existence.
The group believes that God created everything, including dinosaurs, about 6,000 years ago.
Scientists have said the dinosaurs became extinct about 65m years before man appeared.
Ken Ham, president of Answers in Genesis, said the total cost of the ark is more than $100m (Â£77m).
The attraction has been at the centre of controversy in Kentucky, where it was awarded a tax incentive in 2014 worth up to $18m (about Â£14m).
The incentive allowed the park to recoup taxes on money made from visitors.
The tax break was then revoked after it was revealed that Answers in Genesis would only hire Christian staff members. However, the group sued and won.
Opponents of the theme park told the AP it is a violation of separation of church and state.
"Basically, this boat is a church raising scientifically illiterate children and lying to them about science," said Jim Helton, who lives about a half-hour from the ark.
One of the park's biggest critics is science advocate and former television personality Bill Nye "the Science Guy".
Nye debated Mr Ham on evolution in 2014, attracting millions of viewers online.
The video of the debate posted on YouTube by Answers in Genesis has more than five million views.
Following the debate, Mr Ham announced that a bond offering from Williamstown had raised $62m (about Â£48m) for the project, allowing the group to break ground on the site a few months later.
Answers in Genesis estimates that the theme park, which debuted to the public on Thursday, will draw about two million visitors in its first year.
A theme park in the US state of Kentucky has unveiled a 510-foot-long (155 metre-long) wooden model of Noah's Ark.