At a gathering in Portland, state Republican Chairman Charlie Webster announced Romney had won with 2,190 votes compared to 1,996 for Paul, the only other candidate to aggressively compete in the state. Rick Santorum received 989 votes and Newt Gingrich won 349, but neither actively campaigned there.
Webster said any caucus results that come in after Saturday wouldn't be counted no matter how close the vote turned out to be.
"Some caucuses decided not to participate in this poll and will caucus after this announcement," Webster said. "Their results will not be factored in. The absent votes will not be factored into this announcement after the fact."
Maine's caucuses began Feb. 4 and continued throughout the week. But the results announced Saturday accounted for just 83 percent of the state's precincts. Several communities elected to hold their caucuses at a later date.
Caucuses in Washington County scheduled Saturday were postponed until February 18 because of a major snowstorm that blanketed the region. Earlier, party Executive Director Michael Quatrano said county officials were told the results would not count toward the total.
In a televised interview, Webster said there were less than 200 votes in Washington County and he doubted that including them would have changed the outcome.
Speaking to supporters in Portland, Paul expressed disappointment that only a portion of the state's caucuses had counted toward the total.
"I wish all the caucuses had met today," Paul said, adding, "It's almost like we could call it a tie."
Romney was attending a fundraiser in California late Saturday, after campaigning in Maine earlier in the day, visiting caucus sites where he pressed voters for their support.
"I thank the voters of Maine for their support," Romney said in a statement late Saturday. "I'm committed to turning around America. And I'm heartened to have the support of so many good people in this great state."
Romney's victory in Maine, just hours after he won the presidential straw poll at the Conservative Political Action Committee Conference, helped slow a skid that began earlier this week when he lost contests in Missouri, Minnesota and Colorado.
Fouhy reported from Washington. Associated Press Writer David Sharp contributed to this report.