Some states chose not to create their own exchanges, such as Texas, a state with the highest rate of uninsured residents in the nation.
U.S. Health and Human Services Secretary Kathleen Sebelius was in Austin, Texas on Friday as part of a final push to get people signed up for coverage.
Sebelius said roughly 25 percent of Texans, or 5 million people, are without health insurance, and that half would qualify under the ACA's expansion of Medicaid.
Unfortunately, she said, Texas' leadership hasn't accepted the ACA's optional federal funding that would expand Medicaid coverage for working Texans with the lowest incomes.
Sebelius said the state government hasn't been helpful in getting people signed up, and in fact had been fueling misinformation about the program.
Texas Gov. Rick Perry shot back at Sebelius' remarks, saying that the more people learn about the federal health care law the less they like it.
"Yet again, the Obama administration would rather point fingers at other people than accept any of the responsibility for Obamacare's failure," Perry said in a statement.
Al Jazeera and wire services