HELENA – Numbers of Montanans choosing health insurance policies on the “Obamacare” online marketplace surged upward in December, increasing nearly tenfold to 13,135 people.

The sign-ups, through Dec. 28, are an increase of nearly 12,000 policies in a month, up from just 1,382 people at the end of November and a mere 212 at the end of October.

Nationwide, the U.S. Health and Human Services Department reported Monday that 2.15 million people had chosen plans through federal and state-run websites, or nearly seven times the number at the end of November.

“It is a brand new day for health care for millions of Americans and for the millions of families who now finally have coverage,” HHS Secretary Kathleen Sebelius told reporters on a conference call.

The state online marketplace is a key component of the Affordable Care Act, or Obamacare, offering health insurance policies — and subsidies to help pay for them — to people who don’t have access to larger, employer-based group health plans.

The federally run website, www.healthcare.gov, launched Oct. 1 in Montana and 35 other states, had major technical problems during its first two months. However, federal officials say it’s working much better now and has seen strong demand for its policies sold by private companies.

In Montana, 83 percent of those choosing a policy through the marketplace are eligible for a subsidy to offset its cost. The subsidy is available to most households earning between 100 percent and 400 percent of the federal poverty level, or $11,500 to $46,000 for a single person.

Here’s a closer look at the Montana numbers:

— About 18,000 Montanans completed their applications for health-care insurance through the website last year, for households that included 28,000 people.

— About 25,000 of those people have been determined to be eligible to enroll in a marketplace plan, and 13,135 had chosen a policy. They may not have paid their first premium, however.

— Also, 2,051 people who went through the website were found to be eligible for coverage by Medicaid or the Children’s Health Insurance Plan, two government-funded plans that provide mostly free medical coverage.

— About 1.3 percent of Montanans have chosen policies through the Obamacare website – one of the highest rates of any state and well ahead of most of its neighboring states.

The Montana Health Co-op, one of three companies selling polices on the federal website in Montana, sold about 4,500 policies via www.healthcare.gov and another 1,000 outside the website, said Jerry Dworak, president and CEO of the Co-op.

“Let’s just say we’re happy, but not satisfied, at this point,” he said.

Blue Cross and Blue Shield of Montana and PacificSource are the other companies selling policies on the website.

PacificSource had sold about 2,300 policies through the website by Dec. 23, said Todd Lovshin, Montana director for the company. Blue Cross declined to release its numbers, although it appears the company sold slightly less than half the polices chosen through the website in Montana.

John Doran, director of strategic marketing services for Blue Cross, said interest in the policies “really picked up” at the end of last month and that the numbers are “a good start for the first three months of the enrollment phase.”

Blue Cross has given customers until Jan. 30 to pay premiums on policies selected before the end of December; the Co-op and PacificSource are giving those customers until Wednesday to pay their first premium for policies effective Jan. 1.

Doran declined to say how many policies Blue Cross has sold through the website. The company will release those numbers after March 31, when enrollment for 2014 policies ends, he said.