Numbers released Wednesday by President Barack Obama's administration show 36,500 more people in the state signed up through a federal website from Dec. 29 to Feb. 1.
Eighty-six percent of those picking a plan qualified for tax credits to offset a portion of their premium, a higher proportion than 82 percent nationwide. Fifty-six percent of state residents signing up through January were women.
Young adults represented 26 percent of enrollment in Michigan, similar to the national rate.
The website allows consumers to compare and buy insurance. It's a key element of the health law along with an expansion of Medicaid to more low-income adults, which begins April 1 in Michigan.
Most states are still lagging when it comes to sign-ups under the health law, but Michigan is among a dozen high-achievers getting ahead of the game, according to an Associated Press analysis.
The administration has been unable to say how of many of those enrolling for coverage previously had no insurance. Some might have been among the 225,000 Michigan residents whose previous policies were at risk of being canceled because they didn't meet the law's standards.
U.S. Health and Human Services Secretary Kathleen Sebelius said there's still time to enroll by March 31. People risk being fined for not having insurance starting in April.
Erin Knott, state director of Get Covered America, said she expects enrollment to "grow significantly" as more consumers look for health coverage and find out about financial assistance.