Korean workers to relocate to Hawaii to fill the gap in labor on the plantations when the Chinese and Japanese labor became problematic. Relying on Allen's missionary networks to recruit laborers, the HPSA brought the first group of Korean laborers over in January 1903. However, the total number of Korean immigrants to Hawaii in this initial influx numbered just over 7,000. Most of these persons were male laborers, although there were a few with business backgrounds, and approximately 600 were women. Korean migration to Hawaii halted in May 1905, when Japan took over Korea's foreign affairs and restricted migration to Hawaii and the United States.

Missionary involvement in this migration and the church's role in political and social resistance in Korea helped to make the church the most important institution in Korean communities established in the United States. Forty percent of immigrants were Christian before they immigrated and many worked hard to convert their compatriots. In the first two decades of the century over a dozen churches were established in the United States, in large measure as a platform from which to speak out against the Japanese occupation of Korea, and their Korean ministers who were often the political leaders of the community.

Between 1904 and 1907 about 1,000 Koreans entered the mainland from Hawaii through San Francisco. At the turn of the century, when the first Koreans arrived in San Francisco, Chinatown, Ahn Ch'ang Ho, an expatriate intellectual and anti-Japanese patriot, who arrived in San Francisco in 1899, based himself in Chinatown and established the Chinmok Hoe [Friendship Society] in 1903. The Kongnip Hyop Hoe [Mutual Assistance Society], the first Korean political organization was established by members of the Chinmok Hoe was established in 1905. It published the Kongnip Sinpo, the first Korean language publication. In 1909, the Korean National Association was established in San Francisco. While San Francisco served as the port of entry, many Koreans left the city, scattering along the Pacific Coast, primarily doing farm work although there were also dozens of Koreans who worked as wage laborers in mining companies and as section hands on the railroad in Oregon, Washington, Montana, and Utah. The variety of crops grown along the Pacific Coast allowed for something to be harvested year round so farm workers were mobile, following the crops from region to region. Because their numbers were small, Korean workers pooled wages and resources to lease land.

Most of the Korean tenant farmers in Northern California worked in the San Joaquin Valley around the towns of Reedley and Dinuba in the Sacramento-San Joaquin Valley, and in the upper Sacramento Valley.