Stafford shopping development The Grid posted on Facebook news of the long-awaited opening Friday.
The Katy location opened its doors to customers one hour earlier than planned.
SEE ALSO: In-N-Out is finally here. So what's on the menu?
By lunchtime, there were already dozens of cars lined up down the road, waiting in the drive-thru line.
The drive-thru customers were far from the first excited people on the scene. By 4:30 a.m. Friday, two people were already holding their place in line.
"I just love In-N-Out, they make good burgers. I like how they treat their employees," customer Damian Taylor said.
WATCH: Customers arrive 6 hours early for In-N-Out opening day
Over the last several days, restaurant executives said folks can anticipate the opening soon.
RELATED: 7 ways Whataburger wallops In-N-Out Burger
On Tuesday, ABC13 learned there's a race to the finish for two In-N-Out locations, with at least one other site waiting on a construction start date.
In-N-Out is anchoring The Grid, a 350,000-square-foot retail and restaurant development.
SEE ALSO: Much anticipated In-N-Out Burger takes shape at the Grid in Stafford
In Katy, the restaurant will join the Y shops at Park West retail shops.
Employees at the Stafford location were spotted going over equipment and bringing in food items early Friday morning.
In-N-Out Burger reveals highly anticipated second Houston-area location
How does In-N-Out stack up to the Texas favorite Whataburger?
Survey finds In-N-Out Burger dethroned by Chick-fil-A as America's favorite fast food restaurant
Did someone say food?! Houston food lovers, unite!