Fifteen countries and territories are now set to take part in the camps prior to the next edition of the Summer Games: American Samoa, Cook Islands, Federated States of Micronesia, Fiji, Guam, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu and Vanuatu.
Eight sports are currently planned for the camps, including swimming, athletics, weightlifting and wrestling.
As well as ONOC, six other parties signed the MoU.
They are the Japanese Olympic Committee, Fukuoka Prefecture, Yanagawa City, Miyama City, Miyako Town and Chikujo Town.
ONOC President Robin Mitchell was on hand to sign the document on behalf of his organisation.
It is believed to be the first agreement between multiple countries and Tokyo 2020 regarding training camps.
Both ONOC and Fukuoka hope for the camps to begin in the spring.
Six secretary generals from Oceania nations had visited Fukuoka in May to assess the venues in the area.
Among the facilities looked at were the Ryutsu Keizai University in Ryugasaki, including its rugby ground, and Miyako Town's Toyotsu Track and Field Stadium.
A proposal for ONOC members to use training facilities in Fukuoka in the build-up to Tokyo 2020 had already been presented at last year's General Assembly in Fijian town Nadi.