Penny -Yes, I was referring to St. Patrick's "I imagine that the Irish Immigrants just carried on the observance when they arrived here."
True that, but these traditions are dynamic. I don't like to rely on wiki, but their is a pretty concise explanation of what I was getting at earlier here. http://en.wikipedia.org/wiki/Saint_Patrick's_Day#Early_celebrations
I mean, parades and marches are more or less the same thing, and are usually pretty political, the ability to shut down city streets is a big deal, and a sign of legitimacy. Just think of the early gay pride marches, compared to what we have today. Did you know in DC, they have a parade marking the end of slavery, can you imagine how that might be received in certain parts of the country today?
Of course, making the point more vivid is this Orange business we spoke about earlier.
As for July 12, yes, that the big one, but from April through November different Orders and Lodges march observing different victories, or sacrifices. These marches are designed to go right through Catholic areas as much to make a statement about who a person is not, as much as who they are.
As for how I plan to celebrate St. Patty's, well my great grandmother from Finland used to talk about St. Urho, so maybe I'll give that a go this year.