They rose to 8.75 million in the first quarter from 6.97 million a year ago
The firm also posted revenue and profits, which beat analysts' expectations.
GrubHub connects diners and restaurants through online platforms and apps.
Users order through GrubHub and have food delivered by the restaurant.
"More new diners tried Grubhub than ever before in the first quarter. We are seeing clear signs of success from a more diverse restaurant base, broader marketing reach, and continuous improvement of our product," said Matt Maloney, Grubhub CEO.
"We already had the most comprehensive takeout marketplace in the US, and delivery has enabled our restaurant network to grow significantly in both breadth and depth, making Grubhub the place to go for online takeout."
Grubhub works with more than 50,000 restaurant partners in over 1,100 US cities and London.
The Grubhub portfolio of brands includes Grubhub, Seamless, AllMenus, MenuPages, LAbite, Restaurants on the Run, DiningIn and Delivered Dish.