The Monday strike hit the town of Albu Kamal in the early hours of the morning.
The deaths came after 12 women were killed in a strike by the US-led coalition fighting IS in the east of Syria's Raqa province on Sunday, the Syrian Observatory for Human Right said.
The Monday strike hit the town of Albu Kamal in the early hours of the morning, Observatory director Rami Abdel Rahman said.
"They hit a residential area at 3:00 am while people were sleeping, causing the high toll," he said.
He added that IS was using some apartments in the area targeted as local headquarters.
The deaths came after 12 women were killed in a US-led coalition strike on Sunday.
The Observatory said that strike hit vehicles carrying farmworkers home from fields in the afternoon.
IS has lost swathes of the territory it once held in Raqa province, though it still holds Raqa city and some areas to the east.
A US-backed alliance of Kurdish and Arab fighters known as the Syrian Democratic Forces is battling towards Raqa city, the jihadist group's most important remaining Syrian bastion.
The US military said in May that coalition strikes in Syria and Iraq had "unintentionally" killed 352 civilians since it launched operations against IS in 2014.
Rights groups say the actual figure is much higher.