Milwaukee County has begun issuing marriage licenses to same-sex couples.
The U.S. Supreme Court on Monday refused to consider an appeal from five states that were fighting to enforce their bans on same-sex marriage.
Federal appeals court struck down Wisconsin's ban and those in Indiana, Oklahoma, Virginia and Utah. The states appealed their combined case to the Supreme Court, but it has turned away the appeals.
Monday's decision clears the way for gay and lesbian marriages in those states. It also means that same-sex marriage is now legal in 30 states.
The Supreme Court justices did not comment on their decision, but Wisconsin Attorney General J.B. Van Hollen acknowledged in a statement that the legal battle in Wisconsin has ended and same-sex marriage is now legal here. "I encourage everyone to respect the court's action and to administer the law fairly and impartially," Van Hollen said.
His office had fought to preserve the state's constitutional ban prohibiting same-sex marriage that voters approved in 2006.
While the nation's highest court refused to take up the case involving the five states, the justices have not yet ruled on the national issue of gay and lesbian marriage. Attorneys say it may take a split decision in the lower federal courts, before the Supreme Court would take up the issue with national implications. In the Wisconsin case, both federal Judge Barbara Crabb and federal appeals court struck down the state ban.