Juncal Island is an island belonging to Uruguay, located where the Uruguay River empties into the Río de la Plata, a bit above the Uruguayan town of Carmelo.

The much smaller Juncalito Island lies a kilometer north; to the west, separated by the principal channel, lies Portuguese Island (Isla del Portugues), which belongs to the Argentine province of Entre Rios.

From a geological point of view, the island is a mass of riverine affluvient founded on a precambrian granite core.

The island is low and flat, and can be completely submerged during high water.

The vegetation of the island is primarily scrubland, although some trees can be found towards the center.