what county is modesto ca.
Stanislaus County, California. Stanislaus County (/ËstÃ¦náµ»slÉËs/ or /ËstÃ¦náµ»slÉË/) is a county located in the Central Valley of the U.S. state of California. As of the 2010 census, the population was 514,453. The county seat is Modesto. Stanislaus County comprises the Modesto Metropolitan Statistical Area.