By Rob Kampia | Published in The Huffington Post The marijuana policy reform movement reached a significant milestone this month when Illinois Gov. Pat Quinn (D) signed a bill legalizing medical marijuana in the nation's fifth-largest state. With medical marijuana officially on the books in Illinois -- as well as in New Hampshire, where a similar bill was signed into law on July 23 -- a majority of Americans now live in states that have rejected the federal government's policy of absolute marijuana prohibition. Specifically, 20 states and D.C. have legalized medical marijuana, 17 states have decriminalized marijuana possession, and two states have legalized marijuana possession for adults. Of course, there is some overlap between these three categories. But -- even taking into account all of the overlaps -- 53 percent of Americans now live in states that refuse to accept the federal government's position that (1) marijuana has no medical value whatsoever, and (2) all marijuana users should face arrest and jail time. Currently, 37 percent of Americans reside in states that allow people with serious illnesses to use medical marijuana if their doctors recommend such use. This 37 percent figure will likely climb to at least 45 percent by 2017, as momentum is quickly building for medical marijuana legislation in New York and Minnesota. Thanks to the voters of Colorado and Washington -- who approved a pair of ballot initiatives in November 2012 to regulate marijuana like alcohol -- nearly 4 percent of the U.S. population now lives in states where adults can possess up to an ounce of marijuana legally. Alaska is also on track to pass a ballot initiative similar to the Colorado law. The Alaska vote will take place in August 2014. After that, as many as 12 more states could make marijuana legal for adults between November 2014 and the summer of 2017. Seven of them -- Arizona, California, Maine,Massachusetts, Montana, Nevada, and Oregon -- will likely do so by way of ballot measures in November 2016. (Activists in a few of these states have announced initiative plans for November 2014, but none of these initiatives have qualified for the November 2014 ballot.) In the other five states that could end marijuana prohibition by 2017 ¬-- Hawaii, Maryland,New Hampshire, Rhode Island, and Vermont -- change will need to occur via their legislatures. Once all 15 of these states bow out of marijuana prohibition, more than one in four Americans -- including 30 U.S. senators and 142 U.S. House members -- will live in states where marijuana is legal for adults and treated similarly to alcohol. And given the rapid rate at which public support is growing nationwide, it doesn't take a mathematician to recognize that marijuana prohibition is on its way out.