The ceremony took place in front of close friends and family, Los Angeles-based publicist Nanci Ryder said in a statement. It was the first marriage for both.
The bride wore a dress designed by Carolina Herrera, she added.
Chesney, 37, grew up in east Tennessee and now lives on the island of St. John, while Zellweger, who turned 36 two weeks ago, is from Katy, Texas.
The couple met at the Concert of Hope tsunami relief benefit Jan. 15, where Chesney was singing and Zellweger was answering telephones, the syndicated television news magazine "The Insider" reported.
The tiny island of St. John, population 5,000, is more than two-thirds national park and is known for its hiking, pristine beaches and tranquility. It also has an underwater snorkeling trail.
Monday night's reception was being held at Peter Bay, an affluent gated community on the north shore of the island, residents said. The couple and about 45 guests gathered Sunday night at Rhumb Lines restaurant in downtown Cruz Bay, the main town on the island, according to restaurant employees.
Zellweger won a best supporting actress Oscar for "Cold Mountain." She was nominated for Oscars for her work in "Chicago" and "Bridget Jones's Diary."
Chesney currently has two albums on Billboard's top 10 country albums chart, and his single "Anything But Mine" is No. 6 on the magazine's hot country songs list.
Chesney was named Country Music Association entertainer of the year in November, while his "When The Sun Goes Down" was named album of the year. Other of his hits include "Me and You" and "She Thinks My Tractor's Sexy."
According to Country Weekly magazine, Chesney long ago named Zellweger as his favorite actress and was inspired to write his 1999 hit "You Had Me From Hello" after seeing her in "Jerry Maguire."
Zellweger appeared at a recent Chesney concert in Jacksonsville, Florida, presenting him with a margarita and a kiss on stage, Country Weekly magazine reported.
Zellweger has dated White Stripes singer Jack White and "Me, Myself & Irene" co-star Jim Carrey.
By Mat Probasco