Onancock is located at 37°42'41" North, 75°44'57" West (37.711389, -75.749167).
According to the United States Census Bureau, the town has a total area of 1.05 mi2 (2.72 km2). 1.05 mi2 (2.72 km2) of it is land and 0.00 mi2 (0.01 km2) of it is covered by water. The total area is 0.19% water.
Onancock is located in the Eastern Standard Time (EST) timezone, GMT-05:00. It observes Daylight Saving Time (DST).