Common Trees in Illinois: Identification Guide

White Oak (Quercus alba)

As Illinois's state tree, the white oak is a cornerstone of the state's oak-hickory forests, with impressive specimens found throughout Shawnee National Forest in the Ozark Hills of far southern Illinois. This long-lived tree can exceed 500 years in age and provides critical mast for wildlife across the state's remaining woodlands. White oaks are distinguished by their rounded, finger-like leaf lobes and light, ashy-gray bark that breaks into scaly, rectangular plates. They are prolific acorn producers and anchor forest communities from the Cache River wetlands in the south to the Chicago region's oak savannas in the north.

Where to find it: Upland forests, oak savannas, ravine edges, well-drained ridges.

How to identify it:

• Rounded leaf lobes without bristle tips
• Light gray, scaly, blocky bark on mature trees
• Acorns mature in a single season, cap covers about one-quarter of nut
• Leaves turn deep red to burgundy in autumn

Bur Oak (Quercus macrocarpa)

The bur oak is the quintessential prairie-edge tree of Illinois, its thick, fire-resistant bark allowing it to survive the historical grassland fires that swept across the state. Iconic bur oak groves persist at sites like Goose Lake Prairie State Natural Area and along the Des Plaines River corridor. The tree produces the largest acorn of any Illinois oak, with a distinctive mossy, fringed cap that covers more than half the nut. Bur oaks are a keystone species in Illinois's globally rare oak savanna communities, which once covered millions of acres of the state.

Where to find it: Prairie edges, oak savannas, upland ridges, floodplain terraces.

How to identify it:

• Very large acorn with a fringed, mossy cap covering over half the nut
• Deeply lobed leaves with a large terminal lobe and constricted waist
• Thick, deeply furrowed, corky bark
• Branches often have corky ridges along younger growth

Shagbark Hickory (Carya ovata)

Shagbark hickory is one of the most recognizable trees in Illinois's hardwood forests, instantly identified by its dramatic, shaggy bark that peels away in long, curved plates. It is common throughout central and southern Illinois, forming mixed stands with oaks in the state's upland forests. The large, sweet nuts are an important food source for squirrels, wild turkeys, and white-tailed deer. In autumn, shagbark hickory turns a vivid golden yellow, making it one of the most striking fall-color trees in sites like Starved Rock State Park.

Where to find it: Upland hardwood forests, slopes, ridges, well-drained soils.

How to identify it:

• Bark peels in long, flat, shaggy plates curving away from the trunk
• Compound leaves with 5 leaflets, terminal leaflet largest
• Thick-husked nuts that split into 4 sections when ripe
• Leaflets have fine teeth and prominent veins

Black Walnut (Juglans nigra)

Black walnut is one of Illinois's most economically valuable native trees, prized for its dense, dark hardwood and edible nuts. It grows throughout the state, particularly in the rich bottomland soils of the Kaskaskia and Illinois river valleys. The tree produces juglone, a chemical that inhibits the growth of many other plants beneath its canopy, creating a distinctive understory. Illinois is part of the heart of the black walnut's native range, and the state hosts numerous champion-sized specimens in its river corridors and old farmsteads.

Where to find it: Rich bottomlands, stream banks, moist upland slopes, forest edges.

How to identify it:

• Large compound leaves with 15–23 lance-shaped leaflets
• Round green fruits with a thick, fleshy husk that stains hands black
• Dark, deeply furrowed bark in a diamond or interlocking ridge pattern
• Chambered pith visible when a twig is cut crosswise

Sugar Maple (Acer saccharum)

Sugar maple reaches some of its finest expressions in the mesic forests of southern Illinois's Shawnee Hills and the steep ravines of the Illinois and Mississippi river bluffs. Visitors to Giant City State Park and the Trail of Tears State Forest encounter sugar maples that form closed-canopy stands reminiscent of New England forests. The tree provides spectacular fall color in orange, red, and yellow. While Illinois sits at the western edge of the sugar maple's core range, the species thrives in protected, moist north-facing slopes throughout the state.

Where to find it: Moist upland forests, north-facing slopes, ravines, protected coves.

How to identify it:

• Five-lobed leaves with smooth (not toothed) sinuses between lobes
• Paired winged seeds (samaras) with wings nearly parallel
• Gray-brown bark developing deep, shaggy furrows with age
• Brilliant orange, red, and yellow fall color

Eastern Cottonwood (Populus deltoides)

Eastern cottonwood is the giant of Illinois's river corridors, with massive trunks lining the banks of the Mississippi, Illinois, Kaskaskia, and Wabash rivers. It is the fastest-growing native tree in the state, capable of adding 6 feet of height per year in ideal conditions. In early summer, female trees release clouds of cottony seeds that drift through the air along river towns like Grafton, Alton, and Havana. The tree's triangular, toothed leaves flutter conspicuously in the slightest breeze, a distinctive field mark.

Where to find it: Floodplains, river and stream banks, sandbars, disturbed moist soils.

How to identify it:

• Triangular (deltoid) leaves with coarse rounded teeth and a flattened petiole
• Deeply furrowed, pale gray, corky bark on mature trees
• Sticky, resinous, pointed buds in winter
• Cottony seed masses released in early summer

Hackberry (Celtis occidentalis)

Hackberry is an underappreciated but ecologically vital tree across Illinois, thriving in the disturbed, variable soils of the state's river valleys, roadsides, and fence lines. It is immediately recognized by its unique, warty, corky bark with irregular ridges — one of the most distinctive bark textures of any Midwest tree. The small, dark purple berries persist into winter and are critical food for migrating songbirds along the Illinois flyway. Hackberry is one of the most wind- and drought-tolerant native trees in the state and is increasingly used in urban plantings across Chicago's suburbs.

Where to find it: Bottomland forests, bluffs, limestone outcrops, roadsides, urban areas.

How to identify it:

• Bark covered in distinctive corky warts and irregular ridges
• Asymmetrical leaf base, similar to elm but with 3 prominent veins from base
• Small, round, dark purple to black berries on short stalks
• Witch's broom galls — dense clusters of small twigs — often visible in winter

Tulip Tree (Liriodendron tulipifera)

The tulip tree reaches the northwestern edge of its native range in the deep ravines and moist slopes of the Shawnee Hills in far southern Illinois, where it grows alongside magnolias and beech in some of the state's most botanically rich forests. It is the tallest native hardwood east of the Mississippi and produces striking tulip-shaped yellow-green flowers with orange at the base in late spring. The Cache River State Natural Area and Ferne Clyffe State Park protect some of Illinois's finest tulip tree specimens. Its straight, tall trunk and unique four-lobed leaf make it unmistakable.

Where to find it: Moist upland slopes, sheltered ravines, coves in southern Illinois.

How to identify it:

• Distinctive four-lobed leaves with a notched or flat apex
• Large tulip-shaped flowers, yellow-green with orange band at base
• Tall, straight trunk with gray, interlacing ridged bark
• Cone-like seed clusters persist on branches through winter

Tree of Heaven

Tree of heaven (Ailanthus altissima) is one of the most aggressive invasive trees in Illinois, spreading rapidly along roadsides, railroads, and disturbed urban areas throughout Chicago and central Illinois cities. It produces prolific winged seeds and resprouts aggressively from cut stumps, making removal extremely difficult. Its large compound leaves can be mistaken for native sumac or walnut, but the distinctive foul smell when leaves are crushed is a reliable identifier.

White Mulberry

White mulberry (Morus alba), introduced from Asia as a silkworm food plant, has naturalized aggressively across Illinois and hybridizes with the native red mulberry, threatening genetic integrity of the native species. It thrives in forest edges, river corridors, and disturbed soils statewide. The Illinois Natural Areas Inventory flags white mulberry as a significant threat to native forest communities.

Callery Pear

Callery pear (Pyrus calleryana), once widely planted as an ornamental street tree across Illinois suburbs, has escaped cultivation and now invades old fields, forest edges, and roadsides from the Chicago metro area to the Shawnee Hills. It leafs out early, shading out native understory plants, and spreads by bird-dispersed seeds. Illinois has banned its sale as of 2024.

What is the most common tree in Illinois forests?

White oak is the most iconic and historically dominant tree in Illinois's upland forests, along with bur oak in savanna areas. In lowland and disturbed areas, hackberry and eastern cottonwood are among the most frequently encountered species statewide.

Are there old-growth forests in Illinois?

Yes, though rare. Illinois contains remnant old-growth forest patches in the Shawnee National Forest, particularly in the Garden of the Gods area, the Cache River State Natural Area, and a few protected forest preserves in northeastern Illinois. These stands harbor ancient white oaks, shagbark hickories, and tulip trees that predate European settlement.

What trees are native to Chicago's natural areas?

The Chicago region's natural areas, including the forest preserves of Cook and DuPage counties, support native bur oak, white oak, black oak, shagbark hickory, basswood, and hackberry. The North Branch Prairie Project and similar restoration efforts have worked to re-establish native oak savannas that once blanketed the Chicago lakeshore and interior.