The dish can also be ordered as a side for $1.75, Brand Eating reports.
Macaroni and cheese is a staple on most restaurant kids menus around the country, and kids are a crucial set of customers for McDonald's.
The company reportedly gets about 10% of its revenues from Happy Meals.
But its share of young customers has been declining in recent years, according to the food industry research firm Technomic.
Families with a child age 12 or under represented 14.6% of McDonald's customers in early 2015, down from 18.6% in 2011, according to the firm.
McDonald's has been revamping its Happy Meals over the last several years by adding more nutritious sides like apple slices and promoting healthier beverages such as low-fat milk, water and juice.
The company also created a new Happy Meal mascot that promotes healthy eating.
Here's how the mac and cheese looks when ordered as a side:
Macaroni and cheese is also on the McDonald's menu in Japan, where the chain is serving it deep-fried on a sandwich.