Clarksville is located at 39°22'14" North, 90°54'16" West (39.370556, -90.904722).
According to the United States Census Bureau, the city has a total area of 0.82 mi2 (2.13 km2). 0.46 mi2 (1.20 km2) of it is land and 0.36 mi2 (0.93 km2) of it is covered by water. The total area is 43.81% water.
Clarksville is located in the Central Standard Time (CST) timezone, GMT-06:00. It observes Daylight Saving Time (DST).