About 7.4 percent of the city claims some Irish ancestry, according to the 2012 American Community Survey (the most recent data available).
The survey, which is an extension of the U.S. census, allows participants to self-identify in one or two ancestry groups.
In Chicago, 200,724 people claimed Irish heritage in 2012. One-hundred fewer people identified as German (200,624), and 163,966 wrote down "Polish" — about 5.4 percent of the city's 2.7 million inhabitants.
So, how do the Irish stack against other ancestries?
It's hard to tell. A whopping 1.8 million people (more than half the city) were placed into an "other groups" category. This includes people who identified by race terms like "black" or "Hispanic," census officials said.
But St. Patrick's Day isn't all about ancestry.
"People like a party," said Kevin Coakley, who co-chairs the South Side Irish Parade. "St. Patrick's Day comes right at the end of winter. People were cooped up. They want to get out. They want to go enjoy themselves."
Plus, he said, "There's a huge Irish history [in Chicago] — politics, the mayor, across the board."
Irish or not — the culture really resonates with Chicagoans, said Kelly Dougan, outgoing president of the Young Irish Fellowship Club of Chicago.
"The willingness to give back to people is a huge part of Irish culture. We're also very family-oriented and family-based," she said. "And I think that's what Chicago is at it's core. Irish heritage just breathes into that."
As waves of Irish immigrants came to Chicago in the 19th Century, settlers made their mark on the city, Dougan said. They formed tight-knit communities that still exist in Beverly and on the North Side.
"People have a lot of pride when they're Irish," Dougan said. "We tend to have big families who care a lot about each other, who are really energetic."
That enthusiasm has translated into popular events across the city.
In 1979, Coakley and other kids from his neighborhood "walked along our block, 109th and Washtenaw" in the first South Side Irish Parade. The kids' parents hung flags and cheered them on, and the parade grew each year.
People are "proud of where they've come from, and I think that's something that gets passed along to generations," Coakley said.
Do you celebrate St. Patrick's Day? We want to hear about your favorite traditions.