By Mike Dougherty

PHILADELPHIA (CBS) – It was a sea of green in Center City Sunday afternoon for the 245th annual St. Patrick’s Day Parade.

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This grand celebration of Irish heritage dates back to 1771 in Philadelphia, well before green sunglasses or big beer shaped hats were worn by spectators.

Parade organizer Michael Bradley says more than 15,000 people are marching in this year’s parade:

“We have over 200 groups, so this is just a massive event.”

PHOTOS: 2015 Philadelphia St. Patrick’s Day Parade

Jim and Elizabeth have been coming to the parade for a long time. Like many others here, it’s a family tradition for them:

“Yeah, it is a festive day,” Jim said. “I love the Irish dancers. I love to see the symbols of the Irish flag with the American flag together, as you see right now.”

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A lot of people who spoke with KYW Newsradio say their favorite part is watching the little Irish dancers, including Betsy O’Hagan, a teacher who came to see some of her students dance:

“Just saw them. First in the parade. Perfect timing.”

CLICK HERE to watch the full replay of the 2015 Philadelphia St. Patrick’s Day Parade.

Brianna is among the many teens and twentysomethings who came for the party atmosphere.

“I like being with my friends, just walking around and getting a feel for the Irish culture, because I’m not Irish,” she says.

She might be the only one here willing to admit she doesn’t have Irish blood running through her veins.

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Philadelphia’s parade is the 2nd oldest in the nation, behind only New York City.