With the bulk of the returns from Michigan in, Kerry hovered just under 50 percent, well ahead of former Gov. Howard Dean's 17 percent.
This year, Michigan Democrats were able to vote in the caucuses via the Internet and mail. Mark Brewer, the party's executive chairman, said that some 46,000 online ballots had been cast.
Results were delayed, however, by a party decision to extend the voting deadline by two hours in Detroit after voters complained that caucus sites had been closed or moved.
Returns from more than 75 percent of the precincts in Washington showed Kerry with 49 percent of the vote, former Vermont Gov. Howard Dean had 31 percent. The other candidates were in single digits.
Candidate John Edwards, who is hoping to win more Southern contests following his decisive victory in South Carolina, was in Tennessee, which holds its primary Tuesday.
The first-term North Carolina senator said even defeats in the South -- Virginia also has a primary Tuesday -- would not end his campaign.
"This is very much for me a long-term process. It's a war of attrition," he told reporters while campaigning at the University of Memphis. "I'm in it until I'm the nominee."
Retired Gen. Wesley Clark, the only other candidate with a check in the win column following his narrow victory over Edwards in Oklahoma, was in Virginia.
The Dean campaign took a blow Saturday when the leader of the American Federation of State, County and Municipal Employees, Gerald McEntee, announced that the powerful union was pulling its support.
Democratic officials, speaking on condition of anonymity, said McEntee was concerned that Dean's ailing campaign would have a negative impact on the union. Two other service unions, the Service Employees International Union and International Union of Painters and Allied Trades, said they would continue to support the Dean campaign.
Later, the Dean campaign released a statement saying the former governor would continue to focus on the Wisconsin primary on Feb. 17.
"We respect President McEntee and we will work hard to earn the support of AFSCME members in Wisconsin next week," Dean said in a statement. "With the backing of hundreds of thousands of Americans, SEIU and IUPAT we plan to win Wisconsin next Tuesday, regain the momentum our campaign needs, and win the nomination at the Democratic National Convention in Boston."
Ohio Rep. Dennis Kucinich was in Michigan Saturday morning, shaking hands with voters lined up outside caucus sites in Dearborn.
Civil rights activist, the Rev. Al Sharpton, was in the state most of the week, visiting churches, schools and community events.
Kerry, Edwards, Clark and Sharpton all planned to be at the Democratic Party's annual Jefferson-Jackson Day Dinner in Richmond, Va., Saturday night. Dean announced earlier in the afternoon that he would not attend.
As of Saturday morning, Kerry had 274 delegates, Dean had 121, Edwards had 110 and Clark had 82, according to the Associated Press.
There are 128 delegates up for grabs in the Michigan caucuses and 76 in the Washington caucuses.
On Sunday, caucus-goers in Maine will decide who will win the support of its 24 delegates.
A candidate must have 2,162 delegates to win the Democratic nomination.