Yet according to experts, the real St. Patrick didn't even wear green.
The earliest images of Ireland's patron saint show him wearing a dark blue, similar to the color of the former Irish flag.
And St. Patrick isn't even Irish! He was born in the year 387 at Kilpatrick in Scotland. As a teenager, he was kidnapped by Irish raiders and enslaved as a shepherd for several years. He attributed his ability to persevere to his faith in God.
WATCH: Chicago River is dyed green
Timelapse of Chicago River being dyed green
Legend has it, Patrick drove the snakes from Ireland -- but the island never had snakes.
Even the American perception of leprechauns isn't quite right. The Irish fairies of old Gaelic tradition were the size of normal, nonmagical people.
Don't get caught calling the March 17 holiday by the wrong name. It's Happy St. Patrick's Day, Happy St. Paddy's Day, Lá fhéile Pádraig sona duit, or even Happy St. Pat's Day at a push -- but Happy St. Patty's Day it is not.
"Paddy is derived from the Irish, Pádraig, hence those mysterious, emerald double-Ds," Marcus Campbell, creator of PaddyNotPatty.com, wrote on his website. "Patty is the diminutive of Patricia, or a burger, and just not something you call a fella (a man). There's not a sinner in Ireland that would call a Patrick, 'Patty.'"
For those in the U.S. who are looking to celebrate properly -- perhaps with a pint or two -- use the Irish toast "sláinte," which translates to "good health" from Gaelic.