The leaves of Populus deltoides are simple, alternate, toothed and broadly triangular. Buds are often resinous (sticky), but both buds and twigs are much lighter in color than P. balsamifera, the only other Populus species with heavily resinous buds. The bark of young trunks is similar to the pale greenish white color of other members of this genus. When the trees reach a large size the older bark splits repeatedly and becomes deeply furrowed and dark gray or even blackish.

Populus deltoides can grow very quickly on good sites and has the potential to be one of the largest trees in Wisconsin. The flowers of the female aments (catkins) develop into capsules that split open at maturity to release numerous seeds with many hair-like structures which disperse the seeds great distances. The hairs, produced in great numbers, are the source of the name Cottonwood and can be a source of annoyance if they accumulate on window screens or enter open windows. Flowering is in April and dispersal of seeds in late May or early June in the Green Bay area.

Populus deltoides ranges from Vermont to Alberta and Montana and south to Texas and Alabama. The distribution in Wisconsin is mostly southern and it is rare in the northern third. It does best on sunny, wet sites and can establish dense populations of seedlings on exposed, muddy soils.