Arnold is a census-designated place (CDP) in Calaveras County, California, United States. The population was 3,843 at the 2010 census, down from 4,218 at the 2000 census. Arnold is located on State Route 4.
Arnold is named after Bob and Bernice Arnold, who, in 1927 opened the Ebbetts Pass Inn. Prior to that, the community consisted of two large ranches where logging was the main industry. The inn served as a stop for people traveling along the Ebbetts Pass route as well as lodging for those visiting nearby Calaveras Big Trees State Park. In 1928, Camp Wolfeboro was established nearby as a Boy Scout camp and continues to be in operation today. The first post office was opened in 1934.
According to the United States Census Bureau, the CDP has a total area of 14.9 square miles (38.6 km²), of which, 14.8 square miles (38.4 km²) of it is land and 0.1 square miles (0.2 km²) of it (0.47%) is water.