“New Year’s Eve” star Hilary Swank reaffirmed her redneck roots by throwing a hillbilly-style holiday party at the Piano Bar in Hollywood.

The bash was co-hosted by producer Molly Smith, actor Billy Miller and top publicist Stephanie Shaw last weekend, who dressed—along with guests including “Melrose Place” and “All My Children” cast member Colin Egglesfield — in “flannel, trucker hats and bad teeth,” according to a spy.

The invite said, “It’s a Redneck Christmas, Y’all!” and promised “beers and boot scootin’ fun.” Lowbrow libations included Natural Light, Bud Light and Tang-and-vodka punch.

Swank belted out the raucous Beatles’ tune “Birthday” onstage, and posed for pictures with a brunette wearing a tight, camouflage T-shirt reading, “Peace, Love, Racing.” A blond pal rocked a trucker hat, cherry air-freshener earrings and a flannel shirt. Swank, with her boyfriend John Campisi, went for a clingy black top and chic brown leather jacket.

Shaw told us, “We wanted it to be the opposite of the Hollywood formal holiday party. We had Rice Krispies [Treats], Natty Lights and redneck punch. We had tons of beer in buckets on the tables and hot dogs.” Additional cuisine included packets of Nilla Wafers and M&Ms.

“Hilary got into the spirit of it, she had so much fun. We were all going to wear tanks that said ‘Ho ho ho’ — but they didn’t arrive in time, so Hilary was in a cute cowgirl outfit,” Shaw said.

The bash went on until 2 a.m. and featured dancing to country music band Austin Hanks & the Kalifornia King Snakes.

A high school dropout who grew up in a trailer park, Swank has been open about her beginnings. In her 2000 best-actress Oscar speech for “Boys Don’t Cry,” she thanked her mom and added, “It looks like living out of our car was worth it.” When she won again for “Million Dollar Baby,” Swank said, “I’m just a girl from a trailer park who had a dream.”