Marijuana Legality: The Quick(er) Version
A few days ago, I started writing a very long, very detailed post about marijuana legality state by state... and it got eaten by tumblr's drafts features.
This post is going to be the Cliff Notes version of that post.
First off, Wikipedia's Legality of cannabis by U.S. jurisdiction page is an excellent resource for this. It doesn't capture everything, but it captures a lot, and you can always go to linked pages for individual states and/or check the linked sources for more information.
Under federal law, specifically the Controlled Substances Act, marijuana is a Schedule I drug and cannot be prescribed or possessed legally aside from a very tightly-controlled quota for scientific research purposes. This scheduling includes language stating that marijuana "has no currently accepted medical use" and "[t]here is a lack of accepted safety for use of the drug or other substance under medical supervision", which is... arguable.
There is a process for changing drugs, including marijuana, to a less restrictive schedule under the Controlled Substances Act or removing them as a controlled substance altogether. But that process hasn't happened for marijuana so far.
Technically, this supersedes state and local law on the subject; state law can be more restrictive than federal law, but not less restrictive, or else the whole idea of federal law governing the whole country is moot. Theoretically, that means that federal police could arrest anyone, anywhere, for marijuana possession under the Controlled Substances Act, regardless of what local authorities say on the matter.
Realistically, that's highly unlikely. Any case where someone gets arrested for marijuana in a state that says it's okay is practically asking for a Supreme Court case on the matter, and said Supreme Court ruling would inevitable be controversial and divisive, and right now everybody's content to just... pretend the federal law doesn't exist when the state says otherwise. Probably some years down the line such a Supreme Court case will indeed happen and cause a shift to the current murky and unstable status quo, but it's highly unlikely that said Supreme Court case will star you, random marijuana user. (And if it does, well, upside is there's bound to be a bunch of folks willing to represent you for free just to get in on the action!)
Also, the federal police are busy, and hey, if they don't have to worry about marijuana use in a large chunk of the country, that just gives them more time to go after other kinds of federal criminals.
So, if state law's what matters, what do the states say?
Again, I point you to the Wikipedia page outlining exactly this. (It's most of what I'm using for a resource here myself.)
Recreational use of marijuana is legal in 24 states (Alaska, Arizona, California, Colorado, Connecticut, Delaware, Illinois, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nevada, New Jersey, New Mexico, New York, Ohio, Oregon, Rhode Island, Vermont, Virginia, and Washington state), three U.S. territories (Guam, Northern Mariana Islands, and U.S. Virgin Islands), and Washington D.C. Note that Ohio's measure here is newly passed and doesn't actually take effect until December 7, 2023, three days from now.
Commercial distribution is legal everywhere that recreational use is legal except Virginia and Washington D.C.
Personal cultivation for recreational use is legal everywhere that recreational use is legal except Delaware, Illinois, New Jersey, and Washington state.
Recreational use is decriminalized in Hawaii, Louisiana, New Hampshire, and North Dakota.
Medicinal use of marijuana is legal in 38 states (the recreational use ones, plus Alabama, Arkansas, Florida, Kentucky, Oklahoma, Pennsylvania, South Dakota, Utah, and West Virginia), four U.S. territories (the recreational use ones plus Puerto Rico), and Washington D.C.
Medicinal use is decriminalized in Nebraska and North Carolina.
Iowa gets a special shout-out here for allowing medicinal marijuana, but not allowing any actual distributors of said medicinal marijuana in the state; medicinal marijuana patients need to go out-of-state to get their marijuana supplies, but those supplies remain legal upon bringing them back to Iowa.
Personal cultivation for medicinal use is legal everywhere that recreational cultivation is legal plus Illinois, Washington state, Hawaii, Oklahoma, and South Dakota.
Marijuana remains illegal for both medicinal and recreational use in ten states: Georgia (though several cities/counties in Georgia have decriminalized it), Idaho, Indiana, Iowa, Kansas, South Carolina, Tennessee, Texas, Wisconsin, and Wyoming, and also the territory of American Samoa. Everywhere but American Samoa has some exception for CBD oil, though, with limits on the percentage of THC present.
A number of Native American reservations have also legalized marijuana use, either recreational or medicinal.
Most of these laws have restrictions beyond just "it's legal". You might have to be 18 to purchase marijuana, or 19, or 21; there's generally a maximum amount you're allowed to possess, or grow, at one time; medicinal use might be restricted to specific symptoms or conditions outlined in the original law; details may vary about having it in a public place, or about the specific forms allowed.
Also, some laws specifically address potential effects of marijuana use within the state beyond simple criminality. Can marijuana use be considered in a child welfare case, and held against you as a parent? Can use of medicinal marijuana get you fired if you fail a drug test your employer gave you, or just because your employer doesn't like it? Does being fired for using marijuana count as being fired "for cause" for unemployment purposes? Can marijuana use disqualify you from accessing needed health care like organ transplants? Excellent questions! The answers will vary. Or they might not be specified in the original statute at all, which leaves it open for the courts to decide.
If you're going to purchase and/or consume marijuana, please, look up all the details of your local laws on the matter beforehand.