What a way to ring in the fabulous 40s! Reese Witherspoon celebrated her 40th birthday in style on Saturday, March 19, with a star-studded bash at the Warwick in Hollywood that even included a private concert with Taylor Swift.

The Legally Blonde star rented out the entire venue, which is co-owned by nightlife entrepreneurs JT Torregiani and Sylvain Bitton, for the evening of fun, and pals like Kate Hudson, Jennifer Aniston, Justin Theroux, Courteney Cox, Matthew McConaughey, Robert Downey Jr., Isla Fisher, Conan O'Brien, Chris Martin, Chelsea Handler, Tobey Maguire and more turned out for the fete, which had a New Orleans Mardi Gras theme.

“When you take a sh-t load of pictures and you still don’t have it perfect so you go for the ole collage post … Happy Birthday gorgeous girl @reesewitherspoon!!! Love you,” Hudson captioned four photos stitched together in honor of the evening. “#TequillaFirst #PostingLater #SaturdayNight #ImSoExcitedToGetIntoBedIDontEvenKnowWhatToDoWithMyself #NotWashingMyFace #GoodNight.”

An insider tells Us that the woman of the hour headed to her party with “a caravan of three black SUV limos with her family,” including her mom, who had just flown in from Tennessee, and her husband, Jim Toth.

Witherspoon shared a hilarious Instagram video of her and her mom getting pumped up in the backseat of their limo.

Crazy on the dance floor? 🎉🎉🎉 #BirthdayWeekend #MomsInTown 🎂🍧

A video posted by Reese Witherspoon (@reesewitherspoon) on

“Crazy on the dance floor?” the actress captioned the fun video, which featured a disco ball and faux sunglasses superimposed on their faces. “#BirthdayWeekend #MomsInTown.”

Once there, the source said, Witherspoon and Hudson (who was also celebrating her birthday) let loose and got the party started.

“[Hudson] and Reese were tearing up the dance floor having the best time,” the insider told Us. “They were posing for pictures all night long and Erin Foster was interviewing them asking them funny questions.”

At one point in the evening, a drum line marching band even sang "Happy Birthday."

Later on, the night turned into a mini concert, with Swift and Keith Urban taking the stage. Swift, 26, performed an acoustic version of “Shake It Off” while Urban, 48, played “Sweet Home Alabama” as Witherspoon joined him onstage. (Urban’s wife Nicole Kidman was also in attendance.)

“Reese didn’t leave until 2 a.m.,” the source said. “She had the best time and didn’t want the night to end.”

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