More than 2,000 guests attended the Independence Day celebrations and were wowed by the American football pitch specially constructed for the day for the Second Irish American Flag Football Classic.
The game was played between Phoenix Park Pirates and Dublin 8s, comprised of embassy staff and marines and local gaelic football, rugby and soccer players.
The football field included bleachers and giant television screens for live coverage and play-backs.
The American theme was everywhere with red, blue and white decorations covering tables and pathways. There were even Uncle Sam-coloured cupcakes.
The food was a barbecue and guests were treated to as many hot dogs, burgers and nachos as they liked -- all washed down with ice cold beer or juice.
Children were well catered for. They had their own special Kidzone with bouncy castles, a huge inflatable slide, ring toss, face painting and as much free ice-cream as little bellies could hold.
Mr Rooney, whose family owns the NFL's Pittsburgh Steelers football team, emphasised the importance of Irish and American connections but did not go as far as rating the Irish football players against professional American ones.
"I don't think they understand the game," he laughed. "But they are enjoying themselves and that is the most important bit."
Former Tanaiste Mary Coughlan was also at the celebration and soaked up the sun with her daughter Maeve.
"We have very good connections between ourselves and the United States and it is important to keep up those connections," she said.
Also enjoying the festivities was Meath Fine Gael TD Regina Doherty, her husband Declan and their four children. Ryan (6), Grace (9) and Kate (4) were having a ball but the family was really there for Americanophile Jack (11).
Jack has already taken the American naturalisation test online several times in anticipation for the real thing and hopes to go and live in Philadelphia some day.