John T. Dekker (born 1929) is a retired Christian missionary. Dekker was born and raised in Holland before moving to Canada to study at Prairie Bible College. He later studied at the Summer Institute of Linguistics, Grace Theological Seminary, and Reformed Theological Seminary. He and his wife Helen served as missionaries with Regions Beyond Missionary Union. They engaged in medical, linguistic, and church work among the Dani people of Western New Guinea from 1960 to 1981. As a result of their ministry, the Christian population among the Dani grew from 0 to 13,000.