Interesting Facts
Red mulberry is the only native mulberry in the eastern deciduous forest. White mulberry, which is also common in Illinois, was introduced from Asia by the British in the 1700s in a failed attempt to establish a silkworm industry. The white mulberry leaves are the natural food of silkworms. The tree naturalized and white mulberry is now widespread throughout the eastern part of the United States.

Red mulberry is sometimes distinguishable from white mulberry by the presence of hairs on the lower surface of the leaves.  There is also the possibility of hybridization between the two species, which could make them look similar.

Identifying Features

Bark
The trunk of red mulberry is relatively short, and the bark is light gray when the tree is young, becoming yellowish brown or slightly orange/gray as the tree ages. It is finely ridged, with long, scaly plates.
Twigs
The twigs are rough and hairy. 
Buds
The buds are small-about a quarter of an inch long, brown, and pointed. 
Leaves
The leaves are alternate and simple, and are mostly oval-shaped. They are up to 6 inches long, and nearly as broad. They have toothed edges and vary in appearance from heart-shaped (unlobed) to deeply lobed (usually two or three lobes). The leaves are sandpapery or rough above, and hairy (softer texture) on the underside. The upper surface is dark green and dull, and the lower is usually paler. The leaves turn yellow in the fall.
Flowers
Male and female flowers can occur together (as separate flowers) on one tree or on different trees, and appear just as the leaves emerge. The male flowers are closely clustered and green, and the female flowers consist of clusters of spikes. Flowers are greenish-yellow. 
Fruits
The fruits consist of clusters of drupelets (tiny fruits, containing one seed, sometimes in clusters, as in a raspberry), which are red when immature and dark purple at maturity.