Mariemont is located at 39°8'42" North, 84°22'27" West (39.145000, -84.374167).
According to the United States Census Bureau, the village has a total area of 0.86 mi2 (2.23 km2). 0.85 mi2 (2.21 km2) of it is land and 0.01 mi2 (0.02 km2) of it is covered by water. The total area is 1.02% water.
Mariemont is located in the Eastern Standard Time (EST) timezone, GMT-05:00. It observes Daylight Saving Time (DST).