They hid there for days with little food or water.
Mohsen Tawwal, a Yazidi fighter, said he saw a large number of bodies in Kocho on Friday.
“We made it into a part of Kocho village, where residents were under siege, but we were too late,” he told AFP by telephone.
“There were corpses everywhere. We only managed to get two people out alive. The rest had all been killed.”
Amnesty International, which has been documenting mass abductions in the Sinjar area, says IS has kidnapped thousands of Yazidis since it launched its offensive in the region on August 3.
Members of the Christian, Turkmen and other minorities have also been affected by the violence.
In New York, the UN Security Council unanimously adopted a resolution aimed at weakening the jihadists, who control large areas of neighbouring Syria as well as of Iraq.
The resolution “calls on all member states to take national measures to suppress the flow of foreign terrorist fighters”, and threatens sanctions against anyone involved in their recruitment.
When jihadist forces began their Iraq offensive on June 9, peshmerga forces initially fared better than retreating federal soldiers, but the US-made weaponry abandoned by government troops turned IS into an even more formidable foe.
The militants were able to sweep through the Sunni Arab heartland north and west of Baghdad in June, encountering little effective resistance, and Iraqi federal security forces have yet to make significant headway in regaining ground.
In another setback, a roadside bomb on Saturday killed the engineer tasked with repairing a key bridge north of Baghdad, the loss of which has hampered operations farther north.
Many in and outside Iraq say the Shiite-led government was partly to blame by pushing sectarian policies that have marginalised and radicalised the Sunni minority.
Maliki was seen as an obstacle to any progress, and his announcement on Thursday that he was abandoning his efforts to cling to power was welcomed with a sigh of relief at home and abroad.