McDonald’s is still the biggest and fastest burger chain the U.S. with an increase of $1,363,000,000 in sales this year, but some small companies are proving that they are clearly closing the gap, including the Five Guys Burgers and Fries with an increase of $171,500,000 in sales and the Whataburger with an increase of $48,657,000 in sales.
McDonald's
The American fastest growing burger chain is McDonald with $1,363,000,000 (4.4%) increase in sales. It is also the world’s largest chain of hamburger fast food restaurants, daily serving over 64 million customers in 119 countries.

McDonald's has over 31,000 restaurants worldwide
Five Guys Burgers and Fries

The fast food chain, which provides not only burger but also free in-shell peanuts to customers, sees a $171,500,000 increase (37.8%) in sales in the U.S.
Whataburger

The family-owned fast food chain, which has around 700 restaurants in 10 states, has an increase of $48,657,000 in sales (4.3%)
Smashburger

Founded by a former VP at McDonald’s, the company witnesses an increase of $45,703,000 in sales (194.5%). It also serves typical burgers for different areas, including Texas Burger, and Colorado Burger
Hardee's

Though being the second biggest chain on the list, Hardee’s has the lowest percent increase in sales, with just 2.1% or $35,000,000
Culver's ButterBurgers & Frozen Custard

Mainly situated in Wisconsin, Michigan, Illinois, Arizona and Minnesota, the Culver's is very famous for its signature Butterburger, as well as focuses on Midwestern-raised beef and dairy. The sales of Culver’s in the U.S. are $33,064,000 (5.0%)
In-N-Out Burger

With profits from 267 restaurants across the U.S., the In-N-Out Burger sees a $15,500,000 increase in sales (3.4%)
The Habit Burger Grill

With the motto “There’s no substitute for quality,” the Habit Burger Grill is well-known across the U.S. with its signature charburger chargrilled on an open flame. It gets $13,800,000 increase in sales (49.3%)
Jack's

Spreading across the south with locations in locations in Alabama, Tennessee, Mississippi, and Georgia, the Jack’s earns an $11,000,000 increase in sales (11.8%)
The Counter

Boasting more than 312,120 different burger combinations, the Counter has $8,000,000 increase in U.S. sales (19.5%)
Related links:
Top 10 Important Ad Campaigns of McDonald ’s
Top Ten America’s Fast Growing Burger Chains 2011