Somis is an unincorporated community in Ventura County, California. It was established in 1892 by Thomas Bard and D.T. Perkins on a portion of the Rancho Las Posas Mexican land grant. Somis is in the Las Posas Valley: 194  on the south bank of Fox Barranca, just west of Arroyo Las Posas. For statistical purposes, the United States Census Bureau has defined Somis as a census-designated place.