On the eve of the second enrollment period for health insurance under the Affordable Care Act, there is good news, bad news and still many unknowns about the federal law’s impact.

In 2010, President Obama signed legislation, widely known as “Obamacare,” into law with the goal of improving access to health care for millions of Americans.

State and federal officials began working toward that goal in earnest in October 2013, when Americans could begin signing up for health insurance, for the first time, on the marketplaces created by the law.

But one year later, we don’t know exactly how many uninsured Americans signed up for health insurance and, more importantly, who is still without coverage.

The good news: Rates of uninsured people have dropped in every state. In Illinois, for example, the rate fell from about 15 percent in 2013 to about 9 percent in 2014. That’s a huge success.

Most of those who have signed up for coverage, so far, are receiving it through expansion of the Medicaid program. About 476,000 adults have enrolled in Medicaid in Illinois as of September 30, according to the Illinois Department of Healthcare and Family Services (http://www2.illinois.gov/hfs/SiteCollectionDocuments/ACAEnrollmentSummaryData.pdf).

But available data don’t tell us if the law is reaching those who need it most – and in what numbers.

“It’s really hard to say A amount of people were uninsured before, B amount of people got insured, so the number (of uninsured) is now C,” said David Elin, Illinois state director for Enroll America.

Here’s what we can say: There were an estimated 1.8 million uninsured Illinoisans before Obamacare went into effect. About 630,000 of them were Medicaid-eligible adults. More than half of these Medicaid-eligible adults were minorities and about one-third were under the age of 34. (http://data.illinoishealthmatters.org/uninsured/il-medicaidpop-charts.html)

Looking at those who have enrolled in Medicaid, 60 percent are non-white and 42 percent are between 19 and 34. That means that young people and minorities, groups who have traditionally been more likely to be uninsured, have also benefitted most from Medicaid expansion.

“It seems as though people that are Medicaid eligible have taken advantage of that opportunity and enrolled in a higher rate,” Elin said.

Now, the bad news: The numbers aren’t as good for people who were eligible for subsidies to buy insurance in the health insurance marketplace. In the first enrollment period, which ended in March, only about 170,000 people in Illinois enrolled in marketplace coverage with financial assistance. These are people making between 138 percent and 400 percent of the federal poverty line, or less than $94,200 for a family of four.

“We did not do a very good job of going after the working poor,” said Barbara Otto, CEO of Health & Disability Advocates (http://illinoishealthmatters.org/). “And that’s who the Affordable Care Act was created for. That population should be our target. Those are the people we want to make sure don’t fall into the very poor because they get sick.”

Organizations like Enroll America and Health & Disability Advocates, which are working to provide information about health care options and to encourage enrollment in the various insurance options, will have another opportunity to reach the working poor and other uninsured Americans starting on Saturday, when the second open enrollment period for the health insurance marketplace begins.

The data suggest that their job will be even harder this time around. According to a recent poll from the Kaiser Family Foundation (http://kff.org/health-reform/poll-finding/kaiser-health-tracking-poll-october-2014/), 9 out of 10 uninsured Americans don’t even know about the upcoming enrollment period.

And here’s one more thing to keep in mind: Even if every eligible uninsured person in Illinois is enrolled, there will still be more than a quarter-million uninsured Illinoisans. That’s because undocumented immigrants are not eligible for Medicaid or subsidies, putting health insurance out of reach for an estimated 260,000 people in Illinois.

Until people who are undocumented are given access to affordable health care, the goal of universal coverage will not be attainable.

Jonah is a reporter for The Chicago Reporter. Email him at jnewman@chicagoreporter.com and follow him on Twitter @jonahshai.