Polls showed voters favoring initiatives in California, Massachusetts, Maine, Arizona and Nevada.
The proposals treat pot similar to alcohol, limiting it to people 21 and older and barring it in most public places.
In Massachusetts, with 33 percent of precincts reporting, the recreational marijuana initiative was winning 53-57 percent.
In addition, Florida, Arkansas and North Dakota voted on whether to permit marijuana for medical purposes.
In Florida, the medical marijuana initiative appeared to be on the way to victory, with 71 percent support after 66 percent of precincts reporting.
Montana voted on an initiative to ease restrictions on an existing medical marijuana law.
Medical marijuana is available in 25 states.
Alaska, Colorado, Oregon and Washington state already permit recreational marijuana, along with D.C.
Opponents of legalizing marijuana, including law enforcement groups and anti-drug activists, argue legalization of pot endangers the health and well-being of youth, citing studies that indicate damage to cognitive abilities during adolescence can be permanent.
A recent study conducted by an international team of researchers found that people who smoked pot regularly over a long period of time fared worse at midlife compared to their parents.
The study concluded persistent marijuana users are likely to experience greater financial and work-related difficulties in midlife than those who are not addicted at all or have used pot only occasionally. Habituated cannabis users also had more relationship troubles and displayed more anti-social behavior in the workplace. Also noted was a lack of motivation and depression in adolescence, which worsened as use continued.
A Gallup poll in August found that the percentage of American adults who said they smoke marijuana had nearly doubled over the previous three years.
Just 7 percent of adults said they were marijuana smokers in 2013, while in 2016 the figure jumped to 13 percent.
In 2012, Colorado and Washington state were the first to legalize recreational marijuana.
In July, a new study from the American Heart Association found secondhand marijuana smoke may damage blood vessels even more than cigarette smoke.