Research from the Internal Displacement Monitoring Centre (IDMC) reveals that the number of internally displaced people is now twice that of the number of refugees who have crossed international borders.
Ahead of Refugee Week (19-25 June), he claimed 'internal refugees' seem to be forgotten by the international community while the focus remains on those who are forced to emigrate.
He said: "As church leaders from very different contexts, we are bound to say that we, as global neighbours, must do better.
"The UN General Assembly summit in September is an opportunity to address a major failing of the international community that has left the overwhelming majority of displaced people ignored and forgotten."
According to IDMC, 31.1 million people fled their homes and communities – the equivalent of one every second - to find safety in other areas of their own countries. Of those, 6.9 million displacements were caused by conflict, with 2.6 million in Sub-Saharan Africa.
Williams, who is also the chair of Christian Aid, has partnered with bishops from South Sudan and Nigeria to draw attention to internal refugees.
Former Archbishop of Kaduna, Nigeria, Josiah Idowu-Fearon, said 501,000 people in Nigeria were displaced due to conflict and violence in 2016. He claimed much of it was caused by terrorist group, Boko Haram.
He said: "Insecurity in north eastern Nigeria is making food production very difficult, which in turn is driving prices up and causing severe hunger among internally displaced populations.
"With so many people displaced, even proud nations like Nigeria look to the international community for help. The UN needs to address the plight of internally displaced people alongside the ongoing global refugee crisis."
Bishop Emeritus Paride Taban of South Sudan said because of ongoing fighting since 2013,the country has the world's largest growing refugee crisis.
He continued: "Many have fled the country but more than two million citizens have stayed within the borders.
"Very often these people have fled their homes with nothing but the clothes on their backs. They need food, they need shelter, they need peace. They need to return to their homes."
