The county is located in the Arkansas Delta, one of the six primary geographic regions of Arkansas. The Arkansas Delta is a subregion of the Mississippi Alluvial Plain, which is a flat area consisting of rich, fertile sediment deposits from the Mississippi River between Louisiana and Illinois. Large portions of Monroe County are also within the Grand Prairie, a subdivision of the Arkansas Delta known today for rice farming and aquaculture. According to the U.S. Census Bureau, the county has a total area of , of which is land and (2.3%) is water.