Mosier is a city in Wasco County, Oregon. As of 2010, the population was 433. The city was first settled in 1854 and incorporated in 1914. The town was home to the Mosier School, which opened in 1920. It was an 1A school until 1963. From 1964 to 2002, it was part of the Chenowith School District. The town then began a charter school, Mosier Elementary, which serves kindergarten through fifth grade. In January 2003, the district approved a charter school for the town.