TAUNTON — For nearly four centuries, the 150-acre plot has served as Colonial farmland, the sooty neighborhood of Industrial Revolution factories, and most recently, a high-tech office park.

But a stroke of a pen late last year made the parcel something never seen before in Massachusetts: a Native-American reservation decreed in Washington and plunked down many miles away from the tribe’s current home.

Now, its owners, the Mashpee Wampanoag, plan to start work on “First Light,’’ a $500 million casino envisioned to be so massive and so opulent that tribal leaders have been referring to it as the Taj Mahal of New England casinos.

But the bid is running into resistance on two fronts. An anticasino group has enlisted local landowners to challenge the federal decision awarding the land to the tribe. And a second tribe lays claim to that land, saying the Mashpee are interlopers. The historical connection of the Cape Cod Mashpees to this corner of East Taunton, both groups argue, is tenuous to nonexistent.

“The tribe went reservation-shopping and settled on Taunton after taking serious looks at places in Middleborough and Fall River,’’ Tracy Marzelli, a casino opponent who heads the citizens’ group Preserving Taunton’s Future, said last week.

It is a delicate historical question, and if the challenge to the federal government’s decision goes to court, it could take years to resolve. At stake are both a tribe’s dreams and the state’s ambition for a smooth rollout of its bid to collect revenues on gambling, an effort that has already been dealt a series of setbacks.

The 3,000-member Mashpee have spent decades and millions to get federal recognition of their tribe, the necessary first step to the right to open a casino, and $35 million to purchase the East Taunton plot. They now vow to take on all challengers to their intention to open a gambling resort.

The Mashpee do not dispute their opponents’ point that they picked this central site for its promise to deliver customers from Providence, Fall River, New Bedford, and Boston. But they argue that it is well within the tribe’s “aboriginal footprint,’’ which the Mashpee define as most of Eastern Massachusetts, from Cape Ann to Narragansett Bay.

“We are getting back only a small piece of what is rightfully ours,’’ said Mashpee chairman Cedric Cromwell.

The dispute extends beyond any written titles to the land, which began with the arrival of European settlers in the early 1600s. At its foundation are clashing ancestral claims to the site from the Mashpee Wampanoag and the Pocasset Pokanoket tribes.

Cromwell said Wampanoag people have always lived in and around Taunton. “They are our ancestors and that gives us a direct tie to the land,’’ he said.

But Edward Page, chief of the Pocasset Pokanoket, a tribe based in Southeastern Massachusetts, said that his tribe’s ancestors inhabited the land before the 1600s and that they were a distinct people from the ancestors of the Mashpee Wampanoag.

“It was our land,’’ Page said.

Page argues that the true ancestors of the Mashpee never ventured past what is now the Cape Cod Canal and that the modern-day Mashpee “stole’’ their history to support their drive for a casino in a place better suited for it than on the traffic-clogged Cape.

This argument did not sway the Bureau of Indian Affairs, the agency empowered to peer into the past and decide which groups deserve to be recognized as tribes and which lands as reservations. It concluded the Mashpee are descended from a loose confederation of Indian “sachemdoms’’ that dotted the mostly undisturbed 17th century landscape. This Indian nation, under the command of Chief Sachem Massasoit, included the village of Cohannet, in what is now Taunton.

The bureau accepted the version of history that the Wampanoags were then known as the Pokanoket and most of their tribes were driven out of Taunton and other areas after the disastrous King Philip’s War, which was waged by Indians against settlers over land grievances. Some took refuge in Mashpee, a swampy area already sanctioned for Indian inhabitation.

But James Lynch, a researcher who presented the case of the Pocasset Pokanoket to the Bureau of Indian affairs, said the Mashpee Wampanoag had failed to make their case.

“The political influence of the law firms and lobbyists hired by the tribe carried the day for the Mashpee,’’ he said.

In recognition of the high stakes and complicated history, federal law allows opponents of such decisions by the Bureau of Indian Affairs up to six years to file an appeal in court.

Marzelli in December said her citizens group may need all of that time to raise enough money to wage a court battle. The Mashpee respond that they will soon break ground, whether a suit is filed or not.

The possibility that the Mashpee may be locked up in legal limbo for years to come has become a selling point for developers who want to build a casino in Brockton, about 20 miles from the Taunton site.

They argue that the quickest way for the state Gaming Commission to generate revenue for the state is to approve their proposal. The commission is expected to consider whether to issue a commercial license for a casino in that region this winter.

The Mashpee, as a sovereign tribe, are outside state jurisdiction and don’t need such a license.

They have raised a flag over their land on Cape Cod, but their East Taunton office park bears no tribal symbols.

“We are now on tribal land,’’ said Derek Boomer, vice president of a small engineering company that, like all the businesses here, must relocate in deference to the march of history.

“It’s unfortunate that we have to give up this place,’’ he said. “But what can you do?’’

Sean P. Murphy can be reached at smurphy@globe.com. Follow him on Twitter @spmurphyboston.