7 Types of Frogs in Southern Illinois: A Field Identification Guide
September 11, 2026
Tucked between the Shawnee National Forest, the cypress swamps of the Cache River, and the bottomland floodplains near the Mississippi and Ohio Rivers, southern Illinois supports a mix of frog species found nowhere else in the state. Some of the types of frogs in southern Illinois barely cross the region’s northern edge, while others share territory with populations stretching into Kentucky, Missouri, and beyond. This guide covers seven species you’re likely to hear calling from a swamp, prairie pond, or forest puddle if you spend time in the region’s wetlands.
Each species below has a distinct call, body pattern, and preferred habitat, which makes field identification easier once you know what to listen and look for. The quick-reference table gives a snapshot before the detailed profiles that follow.
| Species | Typical Size | Best Time to Hear/See | Signature Habitat |
|---|---|---|---|
| Southern Leopard Frog | 2–3.5 in | Spring through summer | Ponds, ditches, wet fields |
| Bird-voiced Treefrog | 1–1.75 in | April–August nights | Cypress and tupelo swamps |
| Wood Frog | 1.25–2.75 in | Late winter/early spring | Moist woodland pools |
| Green Treefrog | Up to 2.5 in | Summer evenings | Vegetated ponds, trees |
| Pickerel Frog | 1.75–3 in | Spring breeding season | Cool streams, springs |
| Upland Chorus Frog | Under 1.5 in | Late winter chorus | Woodland ponds, southern tip |
| Plains Leopard Frog | 2–3.5 in | Spring through fall | Prairie ponds, wet meadows |
1. Southern Leopard Frog
The southern leopard frog (Lithobates sphenocephalus) is one of the most widespread true frogs in the region and one you’re likely to flush from grass along any pond edge. According to a study guide from the U.S. Army Corps of Engineers, the Southern Leopard Frog averages 2 to 3½ inches in length, and the spots on the back are smaller than the eye diameter, with a body that is light tan, gray-green, or light brown. A useful identification trick is that there is no dark spot on the snout, and there is a light spot in the center of the tympanum.
Listen for its call in wet spring evenings: the call of the male is a short, chuckling trill. The species turns up in various freshwater habitats in Illinois and feeds mostly on invertebrates. As one field guide notes, Southern Leopard Frogs primarily eat invertebrates, such as insects and crayfish. This range extends well beyond Illinois; readers comparing populations across state lines can check the frogs found in neighboring Kentucky for a broader regional picture.
Pro Tip: Southern leopard frogs are easy to confuse with plains leopard frogs. Check the snout first — a clean, spotless snout points to southern leopard frog, while a broken dorsal ridge near the thighs signals plains leopard frog.
2. Bird-voiced Treefrog
Few frogs are as tied to a single southern Illinois landscape as the bird-voiced treefrog (Hyla avivoca). Researchers describe its home turf plainly: the swamps of southern Illinois are enchanting, often making visitors feel as if they have been transported to the most remote areas of the southeast, and within these beautiful remnant bald cypress and water tupelo tree swamps lies a unique inhabitant, the bird-voiced treefrog. It’s also a species biologists are still working to understand, since it is a small, understudied state-threatened amphibian.
Physically, the bird-voiced treefrog is highly variable and can change colors, however it is typically shades of gray and green with yellow-green inside its legs, and has a distinctive white or yellowish spot under its eye. The name comes from its voice — its call is very bird-like, with 2-5 whistles per second. At Cache River State Natural Area, staff note that seldom-seen but often-heard bird-voiced tree frogs haunt the leafy branches of tall cypress trees, their melodious calls considered by many to be the most beautiful of all the frog voices.
Key Insight: Because bird-voiced treefrogs rarely descend from the canopy except to breed, most sightings happen by ear rather than by eye during rainy spring and summer nights.
3. Wood Frog
The wood frog (Lithobates sylvaticus) is a cold-tolerant species that behaves almost like a different animal depending on the season. Per the same USACE field guide, the Wood Frog averages about 1¼ to 2¾ inches in length, the body color is tan or red-brown while the belly is light, and a dark mask is present on each side of the head. That dark facial mask, paired with a tympanum smaller than the eye, makes it fairly easy to distinguish from leopard frogs sharing the same ponds.
Wood frogs favor moist woodlands with permanent or semi-permanent pools, tending to be aquatic in spring and fall but spending most of summer away from water, which makes them difficult to find after the breeding season. In Illinois, the species occurs in scattered pockets, including the southern one-third of the state. One regional frog blog adds that wood frogs are listed by the state as a Species in Greatest Need of Conservation, so any population found in southern Illinois deserves a respectful distance. The call itself is unmistakable: the male’s call is somewhat like the clucking of a duck. Readers curious how this cold-hardy species fares farther north can compare notes with the wood frog populations documented in Iowa.
4. Green Treefrog
The green treefrog (Hyla cinerea) is the frog most people picture when they think of a classic treefrog, though spotting one in southern Illinois takes patience. According to Bird Watching HQ, adults can grow up to 2.5 inches long and have smooth skin, colored yellowish-green to lime green with pale yellow or white undersides. A helpful marker is that white stripes down their sides sometimes have black borders.
Despite its bright coloring, Green Treefrogs can be hard to find in southern Illinois since they spend most of their lives high in trees, and they also can change color based on light and temperature. They come down mainly to breed: during mating season, they visit ponds, lakes, marshes, and streams to breed and lay eggs, preferring bodies of water with a lot of vegetation. The call carries well across water — their breeding call is a repeated, abrupt, nasal “bark,” and sound is typically the best way to locate these treefrogs. This same species turns up further south in states covered in our Mississippi frog guide, where wetter, warmer conditions support larger populations.
Pro Tip: Scan porch lights and window screens on humid summer nights. Green treefrogs often climb toward insects drawn to artificial light, which makes yards near wetlands a surprisingly good place to spot one.
5. Pickerel Frog
The pickerel frog (Lithobates palustris) looks like a close relative of the leopard frogs but carries a defense the others lack. Animal Spot’s Illinois frog roundup states plainly that the pickerel frog is the only poisonous native frog in Illinois. Its skin secretions are mild by amphibian standards but strong enough to irritate predators and can even harm other frog species if they’re kept together in a confined space, which is why handling one and then touching your eyes or mouth is a bad idea.
Visually, pickerel frogs share the general leopard-frog body plan — brown-toned skin with darker blotches — but their spots tend to run in more regular, squared-off rows down the back, and the inner thighs often show a wash of yellow or orange that southern leopard frogs lack. They favor cooler, cleaner water than most leopard frogs, often turning up near spring-fed streams and rocky seeps in the Shawnee Hills. For readers researching amphibian defenses more broadly, our guide to different types of poisonous frogs covers how toxin-producing species compare worldwide, and the pattern shows up again in frog populations documented in our Maryland frog species guide.
Important Note: The pickerel frog’s toxin is not dangerous to humans in typical outdoor encounters, but wash your hands after handling any wild frog, and never keep a pickerel frog in the same container as other amphibians.
6. Upland Chorus Frog
Small and easy to overlook until it starts calling, the upland chorus frog (Pseudacris feriarum) is a species tied closely to the state’s southern tip. A regional herpetology roundup lists its location as the southern tip of Illinois, noting that the Upland Chorus Frog’s stripes on its back are often broken up and can appear as spots, which separates it from more uniformly striped chorus frog relatives.
It’s easy to mix this species up with its closest lookalike further west in the state. The same source clarifies that the Illinois Chorus Frog does not have a white line that extends off the lips while the other chorus frogs do, a small but reliable clue when you’re trying to sort out which chorus frog you’re hearing. Upland chorus frogs typically call earliest in the season, often while ponds still carry a skin of late-winter ice at the edges. Anyone comparing chorus frog diversity elsewhere can browse our broader roundup of different types of frogs for context on how widespread the genus Pseudacris is across North America.
7. Plains Leopard Frog
The plains leopard frog (Lithobates blairi) rounds out the leopard frog trio found in southern Illinois, and it’s arguably the most common of the three across the region. One frog resource focused on Illinois species notes that the Plains Leopard Frog thrives across Illinois, particularly in the middle and southern parts of the state. A separate field guide describes it as a medium sized frog with a tan color and dark spots, found everywhere besides the northern border of the state.
The clearest way to separate it from the southern leopard frog is the dorsal ridge along its back. According to the same guide, plains leopard frogs have a dorsal ridge that runs down their back that has a break and an indent near its butt or thighs — a feature the southern leopard frog does not share. Plains leopard frogs favor open prairie ponds, wet ditches, and agricultural wetlands more than the swampier habitats preferred by bird-voiced treefrogs or pickerel frogs. Readers tracking this species into the Great Plains proper can see how it fares in our Nebraska frog species guide, where it becomes one of the dominant true frogs.
Key Insight: When two leopard frog species overlap, the dorsal ridge is your fastest field check: a clean, unbroken ridge suggests southern leopard frog, while a broken, indented ridge near the hips points to plains leopard frog.
8. Where to Look and What to Respect
Southern Illinois owes much of its frog diversity to the Shawnee National Forest and the wetlands it protects. The forest itself spans Illinois, U.S., near Harrisburg, Illinois and covers roughly 498,616 acres of hardwood forest, wetlands, and the Shawnee Hills. Within its boundaries, the Cache River area and the LaRue-Pine Hills region draw naturalists specifically for reptile and amphibian diversity; as one field ecology writer puts it, the Snake Road area also harbors many species of frogs and toads, salamanders, turtles, and lizards.
Because many of these wetlands sit on protected land, collecting is tightly restricted. Federal guidance for the region notes that in National Wildlife Refuges, Shawnee National Forest, Federal Public Lands, Nature Preserves, County Forest Preserves, and Department of Natural Resources managed areas, it is illegal to collect any species without appropriate permits. If you want to see multiple species in one outing, visiting during a warm, rainy evening in April or May after dark — with a flashlight and a respectful distance from breeding choruses — gives the best odds across nearly all seven species covered here.
Southern Illinois sits at a genuine crossroads for frog diversity, blending species more typical of the southeastern swamps with others that reach their range limits from the prairies and northern woodlands. The full list of frogs found throughout Illinois shows how these seven regional specialists fit into the state’s broader amphibian picture, and for readers curious about the scale of frog diversity worldwide, our piece on how many frog species exist globally puts the local count in perspective. The same wetlands that support these calling frogs also shelter the spiders sharing these habitats, so a slow walk through a southern Illinois swamp rarely turns up just one interesting find.