Antioch is located at 38°0'18" North, 121°48'16" West (38.005000, -121.804722).
According to the United States Census Bureau, the city has a total area of 27.58 mi2 (71.43 km2). 26.95 mi2 (69.80 km2) of it is land and 0.63 mi2 (1.64 km2) of it is covered by water. The total area is 2.29% water.
Antioch is located in the Pacific Standard Time (PST) timezone, GMT-08:00. It observes Daylight Saving Time (DST).