Legal marijuana sales begin in Illinois on January 1.

Marijuana is legal in 11 states for adults over the age of 21, and legal for medical use in 33 states.

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Illinois residents can purchase marijuana legally for recreational use, starting today.

That makes Illinois the second midwestern state to make cannabis broadly available. Dispensaries opened for business in Michigan on December 1.

Illinois Governor JB Pritzker signed a legal marijuana bill into law in June. The bill contains a sweeping criminal justice component, expunging the records of potentially hundreds of thousands Illinois residents who have previously been convicted for possessing marijuana under previous laws. Up to 770,000 Illinois residents may qualify for expungement, according to ABC News.

The bill will also proactively create opportunities for minority business owners to capitalize on the new industry.

Read more: Here's how to land your dream job in the booming cannabis industry

Despite hiccups in New York and New Jersey, marijuana legalization is spreading around the US.

In 2018's midterm elections, Michigan became the 10th state to legalize recreational marijuana, and Utah and Missouri voted to legalize medical marijuana. Deep-red Oklahoma also voted to legalize medical marijuana in 2018, joining numerous other states that have such laws on the books.

Vermont became the first state to legalize marijuana possession — not sale — through its legislature in 2018 as well, rather than via a ballot initiative.

And, President Donald Trump also signed the bipartisan Farm Bill into law in December 2018, which legalized hemp — a plant that's roughly identical to marijuana but doesn't contain THC, a psychoactive compound in marijuana — nationwide.

Hemp is also a source of CBD, or cannabidiol, a popular, if scientifically untested ingredient in many cannabis-infused products.

Eleven states and Washington, DC, have now legalized marijuana for recreational use for adults over 21. And 33 states have legalized medical marijuana.

Read more: Investors are placing huge bets on marijuana as more states legalize THC. Here are the top 25 cannabis startups that have raised the most VC cash.

In October 2018, Canada legalized marijuana federally, becoming the first G7 country to do.

Mexico's Supreme Court also ruled that marijuana prohibition is unconstitutional, paving the way for the country's new leader, Andrés Manuel López Obrador, to follow Canada's lead.

Marijuana prohibition began roughly 80 years ago when the federal government banned the sale, cultivation, and use of the cannabis plant. It remains illegal at the federal level.

Overturning prohibition is one of the few hot-button topics with widespread support.

According to a recent Pew poll, 67% of Americans think marijuana should be legal, and 91% support making medical marijuana legal. Opposition to legalized marijuana has fallen from 52% in 2010, to just 32% as of November 15.

This article was first published in January 2018 and has been updated. Melia Robinson contributed to an earlier version of this post.