As you can see on a map from the Department of Homeland Security (shown above), 27 states and the District of Columbia (in green) currently meet the federal requirements, so you're in the clear if that's where your ID was issued. Meanwhile, 17 other states (in yellow) were granted an extension until October 10, 2018, ensuring their existing IDs can be used at airport security until then.
However, six states (in blue) -- Illinois, Louisiana, Michigan, Missouri, New York, and Rhode Island -- have yet to receive an extension as of this writing and their IDs may no longer be accepted at airport security when the law's current grace period expires on January 22, 2018. (Yes, it's this complicated, unfortunately.) As of now, you can still use an ID that's not REAL ID Act compliant to board domestic flights in every state, but that could certainly change come next year -- and as quickly as January.
"Extensions are granted on an ongoing basis at the discretion of the secretary of homeland security," a DHS spokesperson told Thrillist in an email. "If a non compliant state does not have an active extension at the time of air travel enforcement in January, they will need alternative identification to fly."
In total, 23 states don’t meet the federal requirements and have either received an extension or have requested an extension beyond the January 22, 2018 cut-off date. At this point, it’s safe to assume that every state will receive an extension through October 10, 2018, and potentially additional extensions that will allow travelers to continue using their IDs at airport security with no problems. Hopefully, every state will make ID cards that meet the law’s requirements by October 1, 2020, because that’s when the TSA will no longer accept anything other than a REAL ID-compliant ID or driver’s license.
It's worth noting that five states -- Michigan, Minnesota, New York, Vermont, and Washington -- currently offer Enhanced Driver's Licenses, which the TSA will accept at airport security checkpoints, according to DHS. Getting an EDL can sometimes cost more than a regular driver's license, though. But at least it's better than having to whip our your passport at airport security every time you fly.