Mason continued to travel across the nation preaching and establishing COGIC churches. As African Americans migrated north and west to industrial cities during the Great Migration, he began to establish COGIC churches in the north and, especially after 1940, in the west. Mason sent ministers and evangelists to cities and urban areas outside the South, including William Roberts (Chicago), O. M. Kelly (New York), O. T. Jones Sr. (Philadelphia), E. R. Driver (Los Angeles), and Samuel Kelsey (Washington, D.C.) From these major cities, COGIC spread throughout the country.