The chicken chain offers free meals to those "fully dressed as a cow" and an entrée to those with "partial cow attire," like a purse or an accessory, according the company's website.
The promotion applies to breakfast, lunch, and dinner meals for adults. Children in cow-inspired attire are given a free kid's meal.
Cow Appreciation day has been celebrated on Fridays in past years.
The company moved it to Tuesday because, "Tuesdays are typically slower business days than Fridays, one of the busiest days within the fast food industry," according to Chick-fil-A.
Check out some of the costumes from this morning: