This is a chart of the uninsured rate in America since 2009. And, since 2014, it shows a pretty staggering drop (the data only goes back to 2009, unfortunately, because that's when Gallup started tracking the issue):
The big thing that changed in 2014 is, obviously, Obamacare. There are lots of ways to judge if Obamacare is working: whether it's helping lower health care costs, if it's improving our access to doctors, and (perhaps the holy grail) if it's making Americans healthier. (The New York Times has an excellent package working through many of these issues). This graph shows that Obamacare is accomplishing at least one of its main goals: expanding health insurance coverage to millions of Americans.