The 27-year-old Girls star and the 34-year-old College Humor co-founder tied the knot on Saturday, her rep confirms to PEOPLE. Williams wore a couture gown by Oscar de la Renta.
PEOPLE has learned that the wedding took place at Brush Creek Ranch in Saratoga, Wyoming, and among the 150-200 guests included Williams' Girls co-stars Lena Dunham, Jemima Kirke, Zosia Mamet, as well as pals Katy Perry, John Mayer, Barry Diller, Diane Von Furstenberg, Bruce Springsteen and Late Night's Seth Meyers.
A source tells PEOPLE that Tom Hanks officiated and that Brian Williams walked his daughter down the aisle.
"The magical setting featured a small creek and spectacular views," the source said. "It was a stunning ceremony.
"Guests arrived to gorgeous weather," the source continued. "On Friday, everyone enjoyed the ranch life and did a variety of activities organized by the couple. They had a rehearsal dinner Friday night at the ranch."
Following the ceremony, where guests sat on pillows, the guests moved onto a reception at the ranch.
Mindy Kaling also attended the wedding and shared a photo with Kirke on her Instagram.
"A pit stop at The Friendly Store outside Laramie, Wyoming, with the great Jemima Kirke," she wrote.
Dunham also shared a photo from the festivities with Kirke, who wore a red ensemble and matching floral headband.
Dunham also shared a photo of Kirke driving in what looks like a rural landscape.
Dunham also regrammed Williams' wedding Instagram, writing, "The world's most beautiful bride. The best Girl. Love forever."
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The daughter of former NBC Nightly News anchor Brian Williams postponed her wedding plans when her father was suspended in February for his false statements regarding his coverage of the 2003 U.S. invasion of Iraq.
Brian will have a busy week ahead as he is set to debut as the breaking news anchor for MSNBC on Sept. 22, where he will be covering Pope Francis' visit to the U.S.
The couple met through mutual friends and dated for more than three years before they became engaged in February 2014.
Van Veen completely shocked Williams with the proposal as she told good friend Meyers: "I was completely surprised. A total surprise, the best kind of surprise."
As for Williams' huge engagement ring, "I'm obsessed with it. I stare at it a lot," she added in the same interview.
Reporting by JANINE RAYFORD RUBENSTEIN and JULIE JORDAN