The Chubut valley in Patagonia, Argentina forms the heart of the Chubut Province, the third largest province of Argentina.

The permanent European settlement of the valley began on July 27, 1865 when 153 Welsh settlers arrived aboard the ship Mimosa, with the aim of setting up a Welsh-speaking colony away from the influence of English. The Argentine government had agreed to give them 100 square miles (260 km²) of land in exchange for settling the land for Argentina.

The Mimosa settlers included tailors, shoemakers, carpenters, doctors, brickmaker s, and miners. There were few farmers, which was rather unfortunate particularly when they discovered that the attractions of the area had been rather oversold and they had landed in an arid semi-desert with little food. They had been told that the area was like lowland Wales. After some difficult early years of suspicion and a small amount of violence, the local Tehuelche people established cordial relationships with the Welsh and helped the settlement survive the early food shortages. The settlers soon established Argentina's first irrigation system based on the river Chubut (in Welsh, Afon Camwy or swirling river), irrigating an area 3 or 4 miles (5 or 6 km) to each side of the 50 mile (80 km) long river and creating Argentina's most fertile wheatlands . In the 1880s a railway was built along the valley to facilitate the movement of wheat to the port of Puerto Madryn (originally Porth Madryn, named after a place in Arfon, Wales) on the Golf Nuevo on the southern side of Peninsula Valdés , now a well-known spot for tourists to see marine mammals.

Serious damage caused by floods in the 1890s and 1900s, together with the imposition of conscription by the Argentine government and a lack of unclaimed farmable land caused some of the Welsh settlers to leave for Canada, eventually resettling in the Winnipeg area, but by the end of the 19th century there were some 4,000 people of Welsh descent living in Chubut.

Over the years use of the Welsh language has declined, although there is still contact with Wales, from where teachers are sent to assist in keeping the language alive, and there is some social cachet in knowing the language—even among people who are not of Welsh ancestry.

Principal settlements in the area are Puerto Madryn, Trevelin (=Milltown), Rawson (after the Argentine Interior Minister at the time of the Mimosa), Trelew (=Lewistown, after Lewis Jones, one of the founders), and Gaiman.