North Carolina continues attracting high enrollments for health insurance, with nearly half-a-million people signed up under the Affordable Care Act in the second year of the law’s insurance mandate.

Health insurance coverage has expanded to 492,014 residents according to a Tuesday update from the U.S. Centers for Medicare & Medicaid Services, the agency that administers the national health insurance program.

The state’s enrollment as of March 31 marks a 12.2 percent reduction from the 560,357 residents who had initially selected a health insurance policy. That means that 68,343 people in North Carolina who went through the process of selecting a plan did not pay their first premium and therefore did not buy coverage.

Still, North Carolina ranked fourth in total enrollment nationwide, behind Texas, Florida and California.

North Carolina has developed a reputation for its well-organized network of social welfare organizations and other nonprofits that mobilized “navigators” and other assistants to sign up low-income residents for health insurance under the federal law.

As a result, North Carolina ranked third nationwide for total reliance on federal financial subsidies, with 93.2 percent of ACA enrollees here receiving financial assistance to purchase health insurance.

Only Florida and Mississippi had a greater percentage of enrollees qualifying for the subsidies that are available to people in lower income brackets.

The average monthly subsidy in North Carolina is $316, which is above the national average of $272, and eighth highest in the nation. The highest average subsidy in the nation was in Arkansas, at $536 a month, and the lowest was in Arizona, at $158 a month.

Overall, of the 11.7 million people nationwide who selected plans, 10.2 million made a payment to buy coverage.

The enrollment numbers shift constantly as some people drop out and others sign up for coverage. The Centers for Medicare & Medicaid Services said Tuesday it plans to issue enrollment updates every three months.

Of those who bought health insurance nationwide, 7.3 million enrolled through the federal exchange in the 34 states, including North Carolina, that did not create their own exchanges.

The status of federal subsidies in these states remains unclear while the U.S. Supreme Court mulls a legal challenge to subsidies distributed in states that haven’t created their own health insurance exchanges.

A Supreme Court decision is expected within several weeks and could invalidate federal insurance subsidies for 458,738 people in North Carolina.

The Affordable Care Act requires most Americans to buy health insurance if they already don’t have coverage through their employers or a federal program like Medicare or Medicaid.

The law provides financial aid to people whose household income falls between 100 percent and 400 percent of the federal poverty level.

The law also prohibits industry practices common in past years, such as turning away people with pre-existing conditions, or charging more to customers who have serious illnesses.