Gov. Jay Inslee, U.S. Senator Patty Murray and others celebrated the success of the program and recognized the unprecedented efforts in the state to bring health insurance to people who could not have afforded it in the past.
"There are 600,000 reasons to celebrate: 600,000 Washingtonians waking up this morning with the security of their own health," Gov. Jay Inslee said at a news conference in Seattle on Wednesday.
More than 1 million people have now accessed health insurance through the Washington healthfinder website, officials said.
As part of that total, more than 450,000 adults obtained new coverage under Medicaid, the federal-state program for the poor and disabled. As of the most recent numbers through April 17, two-thirds of those, or about 300,000, were newly eligible for the program, while the rest were previously eligible but did not sign up until the open enrollment period. An additional 455,000 renewed their Medicaid coverage through the state's exchange.
Washington is one of more than two dozen states that elected to expand Medicaid coverage.
"We come into the home stretch with some of the highest enrollment counts in the entire country, and that's because the Affordable Care Act is working," Murray said.
She reminded people that "we're not going back" and that they'll fight Republican efforts to repeal the federal health law.
State officials said Wednesday that they did not yet know how many people are still uninsured in the state.
One-fourth of those who signed up for new plans are young adults age 18 to 34, according to the new data from the Washington Health Benefit Exchange. Many young people appeared to have waited to sign up, with a huge enrollment spike from the 18 to 34 age group coming in the final weeks of open enrollment.
The state has previously reported that 147,000 people signed up for private health coverage, but said the total grew to 164,062 as officials finalized applications after the March 31 deadline. Open enrollment began last October.
Richard Onizuka, CEO of the state exchange, said they didn't know what to expect last fall as they were preparing to roll out the program.
He and others credited the hard work of many in the state, including volunteers, community groups, partners, brokers and health navigators, for the program's success so far.
Most who signed up for private plans were single, the state data shows. More women had enrolled through the exchange than men. About two-thirds of people who began the application process eventually enrolled in a plan.
And the majority of those who enrolled in private plans selected the "silver" plan, which covers 70 percent of health expenses, leaving the patient to cover 30 percent. Meanwhile, less than 10 percent chose the top-level "gold" plan, which covers 80 percent of medical costs.
About three-fourths of people qualified for a tax credit to lower their monthly premium. The average tax credit they received was $276 a month, and the average cost of a private health care plan with a tax credit was $100 a month, officials said.