Marion is located at 37°43'50" North, 88°55'58" West (37.730556, -88.932778).
According to the United States Census Bureau, the city has a total area of 13.52 mi2 (35.03 km2). 12.83 mi2 (33.22 km2) of it is land and 0.70 mi2 (1.81 km2) of it is covered by water. The total area is 5.15% water.
Marion is located in the Central Standard Time (CST) timezone, GMT-06:00. It observes Daylight Saving Time (DST).