The total represented a 1% rise on the 53.4 million that passed through its facilities in 2014 – it's previous best ever year.
December 2015 was also the busiest December in the airport's history, with 4,581,239 passengers, and was the fourth consecutive month of record-setting passenger traffic.
The airport saw a total of five record-setting months in 2015: April, September, October, November, and December.
“Denver International Airport had a tremendous year in 2015,” said airport CEO, Kim Day.
“We celebrated our 20th anniversary, opened the Westin Denver International Airport and an amazing outdoor public plaza, and we saw demand for air travel to and from Denver at historic levels.
"We are so thankful to our passengers, airlines and business partners for an amazing year – but we aren’t done yet. We will continue to seek out new airlines and destinations, elevate the passenger experience and continue our efforts to put Denver on the world map.”
International flights that use the airport’s customs facility had strong gains in 2015, with an increase of 16%, while Canadian preclearance flights declined 22% due to an economic downturn within the oil industry.
That decline caused overall international traffic to be nearly flat in 2015 with 2,192,613 international travellers, compared with 2,208,209 the previous year.
In 2016, the airport will celebrate several new carriers and new non-stop destinations.
Virgin America, a new carrier for DEN, will launch non-stop service to San Francisco beginning March 15. On April 5, United Airlines will begin non-stop flights from Denver to Richmond, Virginia while in May, Lufthansa will begin direct flights to Munich.
Other new services will be launched later in the year by Sun Country Airlines, Air Canada and Southwest Airlines.
• New York's John F Kennedy International Airport pipped it to fifth spot by welcoming 56.8 million passengers in 2015.
Top 5 US airports in 2015