The Affordable Care Act has helped millions of Americans get health insurance. But it’s helping Americans in some parts of the country more than others.

Now, thanks to the U.S. Census Bureau, there’s an easy way to see where.

Obamacare has two big components. one is the creation of exchanges, through which people without access to employer-coverage can buy private coverage.

The other is an expansion of Medicaid, the federal-state program that provides insurance to the poor and disabled.

The law’s architects had hoped, and expected, that people living in every state could take advantage of both. Then the Supreme Court intervened. In a 2012 ruling about a constitutional challenge to the law, the court gave states new leeway to decline participating in the Medicaid expansion.

States with Republican governors or legislatures (or both) were quick to seize on that latitude. They wanted no part of Obamacare, they said, and so declined to participate.

But ever so slowly, Republican officials in some of those states had second thoughts. The federal government picks up nearly all of the cost of new Medicaid enrollees, so for the states it’s a sweet deal financially. It’s more money for doctors and hospitals, and eventually other businesses ― and, of course, critical financial protection and access to medical care for the poor.

One by one, Republican governors started getting their states to join the Medicaid expansion ― either by persuading legislatures or using their own authority. Mostly it was in states like Arizona, Michigan and Ohio ― places that, politically, are not too conservative.

Not every such state has joined, however. And in those states, not surprisingly, the progress on helping people get insurance lags conspicuously. Among the seven states where the Census Bureau found that more than 12 percent of people still didn’t have coverage last year, six were states that rejected the Medicaid expansion. The three biggest holdouts are Florida, Georgia and Texas. Two of the others are also in the South, in which Republicans dominate.

The animated map above, based on information from Tuesday’s annual report on health insurance from the Census Bureau, shows what that means: The law’s effect washes over the country, dramatically reducing the number of uninsured along the coasts and in the upper Midwest, but reaching the South more slowly.

The result is a disparity in how many people have insurance, from state to state. And although that disparity existed even before Obamacare, for a variety of reasons, now the disparity is getting wider, as analysts at the Center on Budget and Policy Priorities noted on Tuesday.

Center on Budget and Policy Priorities

Of course, insurance alone does not guarantee access to affordable health care. But studies have shown that people with insurance generally and with Medicaid specifically tend to be better off financially and probably (but not definitely) healthier, as well.

As the new Census Bureau report shows, some parts of the country can see that effect firsthand. And some cannot.