Al Watkins, an attorney for the couple, confirmed the indictments against Mark McCloskey, 63, and his wife, Patricia McCloskey, 61.
A spokeswoman for Circuit Attorney Kim Gardner declined comment.
The McCloskeys, who are both lawyers, have become folk heroes among some conservatives. They argue that they were simply exercising their Second Amendment right to bear arms, and were protected by Missouri’s castle doctrine law that allows the use of deadly force against intruders.
The case has caught the attention of President Donald Trump, and Republican Missouri Gov Mike Parson has said he will pardon the couple if they are convicted.
The McCloskeys also were featured speakers on the first night of the Republican National Convention. They have accused the “leftist” Democratic St Louis leadership for their plight.
But Ms Gardner, a Democrat, charged the couple with felony unlawful use of a weapon. She said the display of guns risked bloodshed at what she called an otherwise peaceful protest.
Mr Watkins said that addition to the weapons charge, the grand jury indictment includes a tampering with evidence charge. It was not clear what led to that additional count, he said.
The McCloskeys contend the protest was hardly peaceful. They say protesters came onto the private street after knocking over an iron gate and ignoring a “No Trespassing sign”, and said they felt threatened.
The incident happened on June 28 as protesters were walking toward the home of Mayor Lyda Krewson, a few blocks away.
They suddenly decided to veer onto the McCloskeys’ street, prompting the confrontation that was caught on phone video. It showed Mark McCloskey in front of their home armed with an AR-15 rifle and Patricia McCloskey with a semiautomatic handgun.
A police probable cause statement said protesters feared “being injured due to Patricia McCloskey’s finger being on the trigger, coupled with her excited demeanour.”
Nine people involved in the protest were charged with misdemeanour trespassing, but the city counsellor’s office later dropped the charges.
The city counsellor’s office handles lesser crimes and is not affiliated with the circuit attorney’s office.
Mark McCloskey, after a brief court hearing last week, expressed anger that he and his wife faced criminal charges while those who trespassed onto his property did not.
