The first time my grandparents took me out for corned beef and cabbage on St. Patrick's Day in LaSalle, Illinois back in the 1968 I felt cheated.
"Where's the corn?" I asked my grandmother, thinking that I was going to get corn, beef, and cabbage.
"Oh, you don't get any corn," she explained with the patience of a saint. "Corned beef is a kind of meat."
I might not have gotten any "corn" with my corned beef and cabbage, but what I did get, at least what it would turn out to be for me growing up, was the annual tradition of eating this traditional Irish-American meal every St. Patrick's Day. (Turns out that the "corn" in corned beef is actually the process in which the meat is dry-cured; of course, try telling that to a ten-year-old boy to assuage his curiosity. Probably just better to say that they forgot to cook the corn.)
Back in the Illinois Valley (an area comprised of four cities LaSalle-Peru-Oglesby-Spring Valley and other smaller towns, about 90 miles southwest of Chicago) when St. Patrick's Day rolled around many people went out for this traditional meal. There had been a lot of Irish immigrants to the Illinois Valley, many who helped build the Illinois-Michigan Canal. With a large Irish presence in the area it was only natural that the tradition of eating corned beef and cabbage on St. Patrick's Day would become part of the local culture.
Most people went to the American Legion or the VFW for this annual feast; others either went to their neighborhood tavern or prepared it at home.
In the case of my family, at least my grandparents and I, it was going to the American Legion for our corned beef and cabbage. It was one of the few places in LaSalle or Peru with a dining room large enough to accommodate the hundreds of diners who would come for their St. Patrick's Day feast. The American Legion started serving at 11:00 and continued to serve the meal until they ran out, which was usually around 6:00. We always got there early; sometimes when the Legion opened at 11:00 to make sure we would have our piping hot meal.
As for the origins of this dish (sans the corn for wide-eyed curious ten-year-old boys) it is more of an Irish-American tradition than an Irish one.
It is true that cabbage has long been a staple of the Irish diet, but corned beef was not. Instead, the cabbage was traditionally served with Irish bacon. Supposedly Irish immigrants to the US substituted the harder to find and more expensive Irish bacon with the easier to find and cheaper corned beef (perhaps the Irish immigrants got a little help from their Jewish neighbors who pointed them in the right direction of a local deli).
Although some Irish have criticized this traditional meal as being "too plain" it remains to this day in America a popular St. Patrick's Day tradition.