Bucking 31 other states that have defined marriage as between a man and a woman -- effectively banning same-sex marriages within their borders -- voters in Maine, Maryland and Washington said they approve of marriage for all couples.
Nine states and the District of Columbia now have approved same-sex marriage.
In Minnesota, meanwhile, voters defeated an effort to constitutionally state marriage was between a man and a woman.
In Maryland, Attorney General Doug Gansler issued an opinion that the initiative allows county and city courts to take applications for marriage licenses before the law takes effect Jan. 1, with the provision that couples could not become legally married until the effective date.
The same-sex marriage law was signed in Washington state and went into effect in early December. CNN reported a lesbian couple, together since 1977, received the first license in King County shortly after midnight.
"Oh, my goodness!" Jane Abbott Lighty, 77, told CNN, noting she and her partner, Pete-e Petersen, 88, have "been together 35 years and seen all kinds of change."
While the question remains unpopular in the South, same-sex advocates said they see potential wins in several states, including New Jersey, where Republican Gov. Chris Christie vetoed a bill that would have legalized same-sex marriage.
"The pace of the change in opinions has picked up over the last few years," Michael Dimock, associate research director of the Pew Research Center, told The New York Times, "and as the younger generation becomes a larger share of the electorate, the writing is on the wall."
Washington also was one of two states that approved recreational use of marijuana for anyone at least 21 years of age. Colorado also approved the measure while voters in Oregon nixed the measure.
Oregon already allows marijuana use for medical purposes; the question before the voters was whether to direct the state to set up a commission that would have overseen people who grow, process and package marijuana, and license stores to sell marijuana for medical purposes, a review by the National Conference of State Legislatures said. Recreational-use marijuana would have been sold through state-licensed stores at prices set by the commission.
Despite decriminalizing possession of small amounts of marijuana, the U.S. attorney's office in Washington state says possession is illegal on a federal level.
"Regardless of any changes in state law, including the change that [was effective] Dec. 6 in Washington state, growing, selling or possessing any amount of marijuana remains illegal under federal law," statement issued by the U.S. attorney's office in Seattle said.
The Justice Department stance sets up a potential court fight between the federal government and the states, The Washington Post reported. Even though measures violated federal drug laws, the Justice Department so far hasn't provided guidance despite requests from Washington and Colorado, officials said.
Under federal law, marijuana is considered a Schedule 1 drug, the same category as LSD and heroin.
But while possessing marijuana for recreational use in Washington state is decriminalized, buying it remains a felony, CNN reported.
Officials said it could take a year before there are rules developed for growing and selling marijuana under provisions of the initiative.
Until then, growing and selling marijuana will be prosecuted as felonies, King County Prosecutor Dan Satterberg told CNN.
"So I'm not sure where you're suppose to get it," Satterberg said. "If you stumble across some on the street or it falls from the sky, then you can have it. Otherwise, you are part of a criminal chain of distribution."
Voters in five states weighed in on whether the Affordable Care Act would be enforced in their states. The ballot questions generally asked voters to amend their states' constitutions to prohibit forced participation in a healthcare system or the purchase of health insurance, NCSL said. Voters in Alabama, Missouri, Montana and Wyoming approved ACA-related questions; Florida voters rejected it.
Voters in six states considered tax increase proposals, NCSL's review of 2012 ballot measures said.
In Arizona, voters rejected a permanent increase in the state sales tax from 4 percent to 5 percent to help fund education, transportation infrastructure and human services programs. In 2010, voters approved the 1 percent increase, which is scheduled to expire next year.
Transportation projects will benefit by Arkansas voters' approving temporary increases in the tax on diesel fuel.
California had three tax increase proposals on the November ballot and voters approved two of them.
Voters approved Proposition 30 to fund K-12 education and community colleges by temporarily increasing the state sales tax by a quarter of a cent for four years, and the income tax on earnings in excess of $250,000 for seven years.
Rejected was Proposition 38, which also would have increased taxes to fund education
Voters adopted Proposition 39, which modifies the way multistate businesses are treated under California's tax laws by requiring such businesses to calculate their California tax liability based on sales in the state of California.
Missourians rejected a proposition that would have increased tobacco taxes to help mainly fund education.
Voters in Oregon approved a measure that will redirect some corporate tax revenue to K-12 education.
In South Dakota, a measure that would have increased the state sales tax from 4 percent to 5 percent and split the new revenue between K-12 education and Medicaid failed on Election Day.
In other initiatives:
-- Massachusetts voters axed a measure regarding doctor-assisted suicide by a narrow margin.
-- Maryland voted to allow some illegal immigrants to pay in-state tuition at the state's universities.
-- Kentucky voters approved a measure that makes hunting and fishing a constitutional right.
-- North Dakota passed a smoking ban for indoor workplaces.