set up to help IDPs with a grant from Open Doors (Photo: Open Doors)
The ultimatum for Christians to convert to Islam, pay a "protection tax" or face death triggered a mass exodus out of the city.
Up to half a million residents, including around 3,000 Christian families, made the painful decision to leave their homes and their livelihoods in search of safety elsewhere.
Many of them went to the city of Erbil in the Kurdish region of northern Iraq.
According to Open Doors, only 25 Christian families stayed in Mosul, some because they were too old, ill or disabled to flee; some because they converted.
Just a few days after Mosul fell to IS, Open Doors started providing support for the thousands of internally displaced people (IDPs).
Working through local churches and partners, they distributed tens of thousands of food and hygiene packages, financial support for clothing and medicine, and Christian materials, including Bibles.
They also supported churches in running vocational training and trauma care. At the height of the operation, 86 people were employed by Open Doors in the packing and distribution of the food parcels.
"The devastation was huge," said Father Sam, a priest who came to Erbil from Mosul, whose name has been changed for security reasons.
"They were difficult days for me as a priest. To see this huge number of displaced people scattered on the streets, sleeping in churches, gardens and schools. I saw people with just their bags crying in front of me. I felt powerless at times.
"I just encouraged people to stay in their faith and urged them to pray, despite the difficulties."
Creating employment opportunities for the IDPs was a large part of Open Doors' long-term response to the crisis, with microloans distributed through churches and local partners to help families start businesses that would give them a sustainable income.
With the help of these loans, families were able to open up barber shops and start agricultural ventures like small-scale farming and honey production.
The loans have helped those who fled regain a sense of worth and independence.
Nashwan used to work as a stonecutter in Mosul before fleeing with his family when ISIS came. He is now working at a stonecutting factory that was set up using an Open Doors grant.
He is one of 50 full-time staff at the factory, which cuts stones that are being used all across Iraq in the reconstruction effort.
"I had worked for 20 years in stone-cutting, and suddenly I was unemployed," he said.
"I had no means of caring for my wife and three children; they are depending on my income. We worried about our future in this country, especially as we saw so many other families migrate."
Factory overseer Yosef described how employment was an important factor for people in deciding whether to leave Iraq or stay.
"Most organisations just distribute food and give people some money. They eat it, they spend it and it's gone. This project offers long-term hope since it guarantees people's salary for the future," he said.
"All these workers are now able to support their families. We hope this will give them a reason to stay in this country."
Even though many towns and cities have been liberated from IS, the situation remains very difficult, with many homes and businesses destroyed or in need of significant repair.
Living costs are high and finding work remains a challenge. The financial impact on the families is huge, with many struggling to pay rent or buy medicine. Many children still cannot attend school.
Even where schools, many are shortstaffed and in a poor state of repair, needing even basic items like tables, doors, windows and a heating system that works.
Hanging over the heads of Christians is the additional fear that while IS might have lost its grip, it has not disappeared. They worry that hundreds of former IS fighters are simply taking their time to regroup and will strike again.
Open Doors says that violence against Christians in Iraq remains a problem, with attacks, abductions and murders still occurring.
In 2018, Open Doors local church partners repaired 1,051 houses in Iraq, but in reality, many Christians have chosen to remain in camps or other cities for now, too scared to return home.
Father Emanuel Klo told the human rights group that only about 50 to 70 families have returned to Mosul.
"They are all elderly people - no Christian families with children or teenagers have yet returned," he said.
"Establishing a Christian school might attract Christians to return, or having a hospital, and an area for Christians to live in."
Raeid, a former lecturer at Mosul University, is staying in Erbil for now. He feels that Mosul is simply too dangerous to return to.
But he remains thankful for the support he has received that has enabled him to survive through these challenging times.
"I thank all the people who stood with us in our time of need. Your support saved my family and saved Christianity from annihilation in Iraq," he said.