Friday is National Cheeseburger Day, so don't pay full price for your patties. Several restaurants are giving discounts on the greasy, gooey comfort food in observance of the delicious holiday. Swing by after work -- or during, we won't tell -- to take advantage of these promotions.

While hamburgers had been around for decades, the cheeseburger wasn't invented until after 1920. There are various origin stories. One follows Lionel Sternberger, a 16-year-old Californian working at his father's restaurant who decided one day to put a slice of cheese on a beef patty. Another credits the invention to Charles Kaelin, a Kentucky restaurant owner in 1934 who wanted to add tang to his burgers. But it was a third man who patented the name "cheeseburger": chef Louis Ballast in Denver, according to Burger Web.

From that point on, the cheeseburger took off in the United States. McDonald's alone sells about 75 burgers every second, and Americans eat about 50 billion burgers a year, the Huffington Post reported. If you're planning to join them on Friday, check out these deals:

Hurricane Grill & Wings, which has about 80 locations, mostly in the eastern U.S., will let customers create their own burgers for $5.99. Plus, get a free order of garlic and Parmesan fries when you join the Beachcomber’s Club.

Burger 21 is giving free Cheesy Burgers to anyone who downloads its free smartphone app and goes into one of its 17 locations. Once you get the dish, take a photo and tag it with #BCheesy to be entered into a contest to win free burgers for a year.

McDonald's locations in Connecticut and western Massachusetts will offer 69 cent cheeseburgers from 11 a.m. to 7 p.m. Limit four per person.

At M Burger in Chicago, get a free order of fries with the purchase of a cheeseburger. If you're in college, bring a student ID for an additional discount.



DogHaus shops, which are mainly clustered in California, will let you upgrade your burger from a single to a double for free on Friday, instead of paying the normal $1.99 fee.

JerryBuilt Homegrown Burgers near Houston, Texas, will serve the classic and Jerry's burgers for $5, instead of $7.50.

The newly opened BurgerFi in Latham, New York, will give a free sundae to anyone who buys a burger and drink between 11 a.m. and 10 p.m.

In Chalmette, Louisiana, customers who buy a burger meal from Brewster's can receive a free drink.



Mark's Outing, also in Texas, plans to give away free quarter-pound cheeseburgers to anyone who stops by its San Antonio location.

At White Castle, use this printable coupon to get $2 off any 20 sliders. This offer is good through the end of the month.

Johnny Rockets doesn't have a National Cheeseburger Day deal, but if you join its e-club, you automatically receive a free hamburger with the purchase of another entrée and drink.

Similarly, Habit Burger doesn't have a Friday-only deal but it does have one for September one. If you donate $2 or more to the charity No Kid Hungry, you get a free Charburger with cheese the next time you visit.