Somero is mentioned a rural municipality in the year 1449. It became its own congregation when old congregation of Portaa split into Tammela and Somero congregations.
The name in based on that the church was built on rough gravel ridge. The word Somero means rough gravel.
Since the medieval ages there has been a Oxroad running through Somero from the castle of Turku to the castle of Häme. Villages grew along the Oxroad and where it crossed the old roads.
The industrial traditions run from 1750s when Åvik glassfactory was founded and later it grew whole manor community around it. Municipality of Somerniemi merged to Somero in 1977.
Somero swapped from Häme province to Turku and Pori province in the year 1990. At the same time municipality became part of Varsinais-Suomi region. Still in the 90s Somero was considered to be the biggest agriculture municipality in Finland. Fields cover a total of 26 000 hectares. In agriculture the trend has moved from pigs to laying hens base lately. Somero become a city in the year 1993.