Jules Brévié's line divided the Gulf islands between the administrations of Cochinchina and Cambodia, but no formal allocation between the two future countries was ever made. When French Indochina dissolved in 1954 the boundary was left undemarcated and the islands unsettled, and Cambodian nationalists went on claiming the whole Mekong Delta as Kampuchea Krom, historically Khmer land. Talks restarted in 1983; in 1985 both governments agreed to recognise the border as it stood at independence; a treaty followed in 2005 and physical demarcation was completed in 2012. What the line enclosed is substantial: 575 square kilometres, fifty kilometres north to south and twenty-five east to west, mountainous and densely forested, rising to 603 metres at Núi Chúa. The soil is poor and the terrain awkward, so Phú Quốc never fed itself the way the delta does. It made its living from the sea instead.

In the early 1780s, hunted by the Tây Sơn rebellion that had swept his family from power across southern Vietnam, the young prince Nguyễn Ánh twice took refuge on Phú Quốc — in 1782, and again in 1783 after his first hideout was discovered. With him was the French missionary Pigneau de Behaine, who had headed a seminary at nearby Hà Tiên on the mainland since 1767 and became the fugitive prince's advisor and protector; the island's remoteness kept them alive until the pair escaped together to Siam. Nguyễn Ánh survived, and eventually returned to take the country back. He became the Emperor Gia Long, the first ruler to govern a unified Vietnam from north to south. An island that had been a place to disappear became, retroactively, the hinge of a dynasty.

At An Thới, near the island's southern tip, French colonial authorities built a political detention centre in 1949–50. It outlived them. Through the war years the site became South Vietnam's largest prisoner-of-war camp, holding Việt Minh, Việt Cộng and North Vietnamese prisoners in a compound of roughly four hectares — as many as forty thousand people in 1973. Vietnamese call it Nhà tù Cây Dừa, the Coconut Tree Prison. Red Cross inspectors who came in 1969 and again in 1972 wrote down what they saw: prisoners showing the effects of inadequate food, poor medical care and physical beatings. During the Tết Offensive in early 1968, 2,665 men rushed the fenceline and got out; few were ever recaptured. The site is a national historical relic now, and a museum. The reconstructions draw visitors, but the number is what stays with you — forty thousand human beings, on four hectares, waiting out someone else's war.

Nước mắm from Phú Quốc is made from black anchovies salted aboard the boat and fermented six to twelve months in wooden barrels bound with rattan braided in the island's own hills. A good barrel works for sixty years. Quality is graded in degrees of nitrogen — 30°N is high, 40°N premium — and the sauce comes out lighter and sweeter than mainland versions. In 2012 it became the first food from Southeast Asia to win protected designation of origin status in the European Union, an honour that doubled as an admission: by 2014 an industry figure estimated that eighty percent of fish sauce sold as Phú Quốc was counterfeit. The island's other export resists bottling. The Phú Quốc ridgeback is one of only three ridgeback breeds on Earth, alongside the Rhodesian and the Thai, named for a strip of spine hair that grows against the grain in shapes owners classify as sword, saddle, arrow or music note. The dogs have webbed feet, swim without persuasion, and often carry a blue-tinged tongue.

The international airport that opened on 2 December 2012 south of Dương Đông runs two runways, 3,000 and 3,300 metres, long enough for wide-bodies. Vingroup and Sun Group supplied the rest: the Grand World resort town with its free electric buses, a golf course, a casino, a safari park in the north, and in the south the enormous facades of Sunset Town. The population has climbed from around 103,000 in 2012 to 157,629 in 2025. On 16 June 2025 Phú Quốc stopped being a district of Kiên Giang province and became a special administrative zone under An Giang. Vietnam will host APEC here in 2027, and the airport passed to Sun Group in November 2025 to be enlarged in time. The beaches that made the island's reputation now come with a caveat — beyond the resort frontage, plastic collects faster than anyone clears it — and the quiet red-dirt roads of the guidebooks are becoming a four-lane highway.