Delaware governor Jack Markell has signed into law a bill decriminalising possession and private use of small amounts of marijuana. The move follows the lead of nearly 20 states that have eased penalties for personal consumption, state media reported on Thursday.

Individuals in Delware will be allowed to possess up to an ounce of marijuana, and to use it privately without facing criminal sanctions. Police could still confiscate the drug, according to Delaware Online, the News Journal.

The statute also will reduce the penalty for using marijuana in a public place to a $100 civil fine. Under previous Delaware law, simple marijuana possession was a misdemeanor punishable by up to six months in jail and a maximum fine of $1,150.

The law will take effect in six months’ time. Markell, a Democrat, signed the measure almost immediately after the state senate, voting along party lines, gave it final legislative approval.

According to the Journal, the Democratic-backed bill cleared the state legislature without a single Republican vote in either the house or senate.

Not counting Delaware, 17 states have passed laws to decriminalise personal marijuana use and possession in small amounts, according to the National Organization for the Reform of Marijuana Laws, a lobbying group.

Delaware is one of 23 states, along with the District of Columbia, that allow the use of pot for medical reasons. Voters in Colorado, Washington state, Oregon, Alaska and Washington DC have approved ballot measures legalising cannabis for adult recreational use.

Marijuana remains classified as an illegal narcotic under US federal law.