Orinda is a city in Contra Costa County, California, United States. The population was 17,643 at the 2010 census, and was estimated in 2012 to have increased to 18,342. Orinda was ranked 2nd most friendly town in America by Forbes. The town is located just east of the city of Berkeley and is home to many affluent suburban professionals who commute to downtown Oakland, San Francisco, and Walnut Creek.