According to Failte Ireland, while the Guinness site, located in the heart St. James's Gate Brewery ranked first with tourists, Dublin Zoo came in second, attracting crowds of more than 930,000 in 2008.
The Cliffs of Moher in County Clare ranked at third, with 808,000 visitors last year.
The famous 700-foot cliffs are currently in the running to become one of the New Seven Wonders of the World in an international competition.
Bord Failte says that visitor numbers could increase by as many as 350,000 per year if the attraction is chosen.
Out of the 20 most visited fee-paying attractions in Ireland, over half were located in Dublin, which some say highlights the lack of quality tourist sites outside of the capital.
Fáilte Ireland's director of business development and investment Paul Keely commented on the organization's findings, saying that cultural and historical visits are on the top of most Irish tourists' lists, with almost 3.4 million overseas visitors traveling to Irish culture sites.
In fact, 51 percent of visitors to Ireland cited culture or history as their reason for choosing the Emerald Isle as a vacation destination.
"Despite the difficult year and downturn, these figures highlight once again the popularity of our visitor attractions and the integral part they play in the overall visitor experience," Keely said.
"With cultural tourists spending almost double the amount of a city-break tourist, it is estimated that the cultural tourism sector is worth 2 billion euros to the Irish economy every year."
This year's tourism statistics will show a major drop in the number of overseas visitors to Ireland, which were down by more than 10 percent in the first half of 2009.
The Irish tourism industry has admitted it has been one of the worst periods in its history, as Ireland welcomed around 400,000 less visitors than usual between January and June.