The Carlsbad street fair is a one day event that happens twice a year- on the first Sunday in November & May- in Carlsbad, CA. With 900 plus vendors and over 100,000 people in attendance, some would say this is the largest street fair in the U.S.
I'm not sure if this really is the largest street fair in the nation- but my husband and I attend the November fair every year for our Christmas shopping. We find over a dozen unique and hand crafted items for gifts at great prices. There is also plenty of food and there are even rides for children!
Tip: Don't even try parking in the vicinity. There's shuttle parking near the event at the Poinsettia train station where you can park and take the shuttle for free. There's another train stop that is right next to the event, so you could also take the train.