White Poplar - Populus alba
Also commonly called "silver poplar."  Willow Family: Salicaceae.
Poplars have wind-pollinated catkins and leaves whose broad blades have long petioles which may be flattened at one end. Their shoots bear terminal buds, and all their buds have overlapping scales. Hybrids grow more vigorously and provide better timber than their parents.

White Poplar - Populus alba

Dark green, glossy poplar leaves toss in the slightest breeze, revealing silvery-white undersides. These trees are relatively rare here near Chicago. I'm not sure why.

White Poplar bark is whitish-grey and smooth above, becoming rough and furrowed at base (shown).

The Willow family of trees (Salicaceae) has 350 or so species of willows and poplars, which are mainly natives of the Northern Hemisphere. The one uniting feature of all Salicaceaes is their flowers; they have neither petals nor sepals but are borne in catkins that usually appear with or before the tree's new leaves. Both willows and poplars prefer moist sites and hybridize so easily identification is sometimes difficult. These trees were growing along the banks of a small creek, along with various willows.

These white poplars are 80 feet tall, with 2-foot diameter trunks. White Poplars are native to Europe, Asia, and North Africa; they were introduced to North America during colonial times. They grow rapidly and spread readily by root sprouts - so readily they often become undesirable as weeds. Along with Quaking Aspen, white poplar belongs to a group of poplars with smooth barks and coarsely serrate leaves.