But surveys estimate that nationally, about a third were previously uninsured, and "there's no reason to think things would be different in Utah," said Jason Stevenson, communications director for the consumer advocacy group, Utah Health Policy Project (UHPP).
About 380,000 Utahns were estimated to be uninsured in 2013.
The late surge in interest shows the president's health law finishing strong despite a rocky start, Stevenson said.
"People are taking a look at what healthcare.gov offers and they like what they see," said Stevenson, who expects sign-ups to continue. "We may find people who have insurance re-evaluating their coverage and signing up because they're getting a better deal."
Indeed, 87 percent of Utah's exchange consumers received federal financial assistance, according to the U.S. Centers for Medicare and Medicaid.
And 33 percent are among the coveted age group of 18- to 34-year-olds.
"Those people who think they're invincible are now getting into the insurance market, which will eventually lower costs for the rest of us," said former Salt Lake County Mayor and state Democratic Party chairman Peter Corroon.
An exchange customer himself, Corroon said he's paying about the same as he was before a job switch thrust him into the private marketplace. Under the old rules he would have been shut out of coverage due to pre-existing conditions, such as a former hip injury and high blood pressure.
A hindrance to full realization of the Affordable Care Act's benefits, he said, is Utah's dithering over whether to expand Medicaid. Doing so would extend coverage to more than 100,000 uninsured, working poor adults and reap billions in federal funding.
Utah Gov. Gary Herbert is pushing for a private-option alternative using federal dollars to buy private coverage, but he needs the Obama administration's blessing and support from ranking Republican lawmakers.
In the 309 days since the Jan. 1 date for expanding Medicaid, the state has forgone $19.2 million in federal funds, according to a "Medicaid expansion clock" created by Utah Democrats.
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By the numbers
Since HealthCare.gov launched on Oct. 1, 2014:
84,601 • Utahns have signed up.
10,384 • more Utahns signed up for Medicaid and Children's Health Insurance Program via the exchange than would have been typical prior to its launch.
Too late to enroll?
With a few exceptions, the marketplace www.HealthCare.Gov is closed until the next sign-up period, which starts Nov. 15.
But if you move to a new state, have a baby, get married or lose job-based or public health benefits such as Medicaid, you'll be eligible for a special enrollment period.
Individuals have 60 days from the time of such "qualifying life events" to pick a plan.