Earliest signs of habitation on the area have been dated to 1200 BC. Various different writings of the name in documents of the 15th century at the
Turku Cathedral are
Harianwalta,
Hariawalta,
Hariaualdastha,
Harianwaltha and
Harianwaltaby. The name is supposed to originate from the speculative Proto Germanic name ''
, composed of the speculative words *harjaz
("army") and *waldaz
("authority"). It is believed that either a person named Harjawaldaz or a warrior band settled or lived in the area. The earliest known written occurrence of the name is from Tacitus on the first century, Chariovalda''. Different adoptions of the same name are
Harald,
Hérault and
Harold, but Harjavalta is closest to the reconstructed original. In 1670, the villages of Harjavalta formed their own
chapel parish, but the official status of an independent congregation began to be sought about 200 years later. Harjavalta's application for its own
pastor was granted in 1868, and the decision was implemented in 1878. The new independent
parish had about 1,600 members. The
great famine years in the 1860s doubled mortality in Finland, but on the scale of Finland as a whole, Harjavalta did little to avoid this ordeal. The act of 1865 on the municipal government led to the formation of the
municipal council and the municipal government also in Harjavalta in 1869. This is considered to be the year of birth of the municipality of Harjavalta. The first
school building was acquired in 1885, when the municipality bought the Kreetala
farm, the main building of which became Harjavalta's first
folk school. ==Transport==