And of the 17 states that posted enrollment above or equal to the overall average, about half are on the federal exchange.
Massachusetts, which runs its own exchange, is last on the list at 5 percent. However, the state instituted its own health-care reform in 2006, and 97 percent its residents were already insured before ACA.
Rounding out the bottom five are South Dakota (5.7 percent), Iowa (5.9 percent), North Dakota (6.8 percent) and Oklahoma (7.4 percent). All four of those states more than doubled their numbers in January and February compared with the first three months of open enrollment.
In fact, 28 states more than doubled their enrollments in the first two months of 2014, compared with the October through December period. Among the notable increases: Florida jumped from 6.2 percent enrollment to 17.4 percent; Idaho moved from 9.9 percent to 21.7 percent; Mississippi more than tripled enrollments from 2.7 percent to 8.6 percent; and Texas increased from 3.8 percent to 9.4 percent.
(Read more: Watch out for late fees—no more Obamacare delays)
Still, most states are well below their CBO targets, with only Connecticut and Rhode Island having actually reached those projections for the end of February.
Access Health CT CEO Kevin Counihan cited great marketing, consistent website function since Day One and an easy enrollment experience as reasons for Connecticut's success.
Counihan said the exchange scaled back its technical requirements by 30 percent nine months before the launch. "We moved from making it a Cadillac to a Ford Focus," he said. "It's not a very sexy car, but it runs."
(Read more: Obamacare: ACA enrollment just 4.2 million by Feb.)
In fact, things are going so well, he's already looking ahead to the fall enrollment period. "Not to say we're taking our eye off the ball in March. We're not. But this thing is cranking. We need to start focusing on renewing business, making the experience even easier. One of the goals is that it keeps getting easier every year," he said.
(Note: The table is based on data from "Health Insurance Marketplace: March Enrollment Report," Department of Health and Human Services, released on March 11 as well as more current data reported directly by state-based marketplaces and "State-by-State Estimates of the Number of People Eligible for Premium Tax Credits Under the Affordable Care Act," Kaiser Family Foundation, Nov. 5, 2013.)
UPDATE: The text of this story was updated to include a comment from CMS.