Both sides in the legal dispute over the Mashpee Wampanoag tribe’s plan to build a $1 billion casino in Taunton expressed confidence that they will prevail Monday after an hourlong hearing before a federal judge.

US District Court Judge William G. Young promised a quick decision in the lawsuit, which was filed by a group of Taunton property owners in February. The suit contends that the federal government erred when it designated the casino site as a Native American reservation last year. Federal law allows tribes to open casinos on reservations, and the Mashpee began construction on the casino in the spring despite the pending lawsuit.

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Young said he would probably issue a decision by month’s end. The hearing revolved around the interpretation of the 1934 Indian Reorganization Act. In 2009, the US Supreme Court ruled that only tribes under federal jurisdiction as of 1934 could be eligible to have reservation land. The Mashpee did not gain federal recognition until 2007. But in ruling in favor of a Mashpee reservation, Interior Department officials interpreted the 1934 law differently. It is that ruling the Taunton property owners are challenging. “We remain optimistic” of a favorable ruling, said David Tennant, the lawyer representing the property owners, who say they object to their neighborhood becoming the destination for tens of thousands of gamblers each month.Lawyers for the Interior Department asked Young to consider what Congress intended when enacting the 1934 law based on statements made by lawmakers at the time. Advertisement “We have been pursuing our sovereign rights for hundreds of years, and will continue to do so,” said Cedric Cromwell, the Mashpee tribal chairman. “Thankfully, the judge clearly understands the complexity of the issues involved. We remain confident moving forward.”Both sides have said they will appeal an adverse ruling to the US First Circuit Court of Appeals, and if necessary to the US Supreme Court.If Young rules in favor of the property owners, he could halt construction on the casino while appeals move forward. In April, the state Gaming Commission voted down a $677 million casino in Brockton, just 20 miles away from the Taunton site. The City of Taunton filed a brief in favor of the casino, which Young accepted over the objection of the lawyers for the property owners.“We are pleased Judge Young allowed the City of Taunton to present its argument to the court, as that represents the majority of Taunton residents who voted overwhelmingly in favor of First Light,” Cromwell said.Sean P. Murphy can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Follow him on Twitter @spmurphy-boston.