Colorado is now one of two states in the nation that has a legalized marijuana law.
Amendment 64 led late Tuesday night with 53.3 percent voting yes and 46.7 percent voting no, with 1,863,535 votes or about 66 percent of active voters counted.
The Denver Post projected the amendment would pass.
In Montezuma County, voters said no way, voting against the amendment 6,127 to 5,882.
The county commissioners passed a resolution opposing it and Sheriff Dennis Spruell had vehemently voiced his opposition against the amendment leading up to the election.
The amendment will allow those 21 and older to purchase up to one ounce of the drug at specially regulated retail stores. Possession would be legal but not public use.
Adults could grow up to six marijuana plants in their homes. It also sets up a direct challenge to federal drug law, which regulates it as an illegal substance. Federal authorities have not said how they will respond.
Gov. John Hickenlooper released a statement Tuesday night concerning the passage of Amendment 64.
The voters have spoken and we have to respect their will. This will be a complicated process, but we intend to follow through. That said, federal law still says marijuana is an illegal drug so dont break out the Cheetos or gold fish too quickly.
Voters in Washington state approved a similar measure Tuesday while voters in Oregon failed to pass the issue.