Reserve is located at 30°3'12" North, 90°33'5" West (30.053611, -90.551389).
According to the United States Census Bureau, the city has a total area of 17.12 mi2 (44.33 km2). 16.07 mi2 (41.61 km2) of it is land and 1.05 mi2 (2.72 km2) of it is covered by water. The total area is 6.14% water.
Reserve is located in the Central Standard Time (CST) timezone, GMT-06:00. It observes Daylight Saving Time (DST).