From the beginning of the war, the Koreans organized militias that they called "righteous armies" (Korean: 의병) to resist the Japanese invasion. These fighting bands were raised throughout the country, and participated in battles, guerilla raids, sieges, and the transportation and construction of wartime necessities.

There were three main types of Korean "righteous army" militias during the war: the surviving and leaderless Korean regular soldiers, the patriotic yangbans (aristocrats) and commoners, and Buddhist monks. By the summer of 1592, there were about 22,200 Korean guerrillas serving the Righteous Army, who tied up much of the Japanese force.

During the first invasion, Jeolla Province remained the only untouched area on the Korean peninsula. In addition to the successful patrols of the sea by Yi Sun-sin, the activities of volunteer forces pressured the Japanese troops to avoid the province in favour of other priorities.