Geography of DeKalb County, Illinois

By | March 13, 2024

Geography and Climate of DeKalb County, Illinois

DeKalb County, situated in the north-central part of the state of Illinois, is a region characterized by its diverse geography, fertile farmland, and rich history. Encompassing an area of approximately 631 square miles, the county is home to a mix of urban, suburban, and rural landscapes, with rolling prairies, meandering rivers, and picturesque lakes. From its vibrant communities to its natural beauty, DeKalb County offers residents and visitors alike a blend of modern amenities and scenic charm. Check topschoolsoflaw to learn more about the state of Illinois.

Topography and Landforms:

DeKalb County’s topography is relatively flat, with gently rolling hills and fertile plains predominating the landscape. The county is situated within the Central Till Plain region of Illinois, a vast expanse of flat, fertile land that stretches across much of the state’s northern and central regions.

Elevations in DeKalb County range from around 650 feet above sea level in the southeastern part of the county to around 900 feet above sea level in the northwestern part. The terrain is generally gentle, with occasional low-lying areas and small hills dotting the landscape.

The county is intersected by several rivers and creeks, which play a vital role in shaping the geography and providing water for irrigation, recreation, and wildlife habitat. The Kishwaukee River, one of the county’s main waterways, flows through the central part of the county, meandering through scenic valleys and wetlands on its way to the Rock River.


DeKalb County experiences a humid continental climate, characterized by hot, humid summers and cold, snowy winters. The county’s climate is influenced by its location in the Midwest, as well as its proximity to the Great Lakes.

Summers in DeKalb County are typically warm and humid, with average temperatures in July ranging from the mid-60s to the low 80s Fahrenheit. High temperatures can occasionally exceed 90 degrees Fahrenheit, particularly during heatwaves, but generally, summers are pleasant and sunny, with occasional afternoon thunderstorms providing relief from the heat.

Winters are cold and snowy, with average temperatures in January ranging from the mid-teens to the low 30s Fahrenheit. Snowfall is common in DeKalb County, with several inches of snow accumulating each winter. Snowstorms and blizzards can occur, particularly in the northern part of the county, leading to hazardous driving conditions and school closures.

Spring and fall are transitional seasons marked by fluctuating temperatures and changing weather patterns. These seasons offer mild temperatures, blooming flowers, and vibrant foliage, making them ideal for outdoor activities such as hiking, birdwatching, and exploring the county’s natural beauty.

Rivers and Lakes:

DeKalb County is intersected by several rivers and creeks, which provide important habitat for fish, wildlife, and plant species. The Kishwaukee River, one of the county’s main waterways, flows through the central part of the county, offering opportunities for fishing, kayaking, and wildlife viewing.

In addition to the Kishwaukee River, DeKalb County is home to numerous smaller creeks and streams, including the South Branch Kishwaukee River, the North Branch Kishwaukee River, and the Sycamore Creek. These waterways provide habitat for a variety of fish species, including bass, catfish, and trout, as well as opportunities for outdoor recreation and relaxation.

While DeKalb County is not known for its natural lakes, there are several man-made lakes and reservoirs in the region. These lakes, including Pierce Lake and Shabbona Lake, offer opportunities for boating, fishing, and picnicking, as well as birdwatching and wildlife photography in the surrounding wetlands and forests.

Vegetation and Ecosystems:

The natural vegetation of DeKalb County consists primarily of grasslands, woodlands, and wetlands, with a mix of native and introduced plant species. Historically, the county was covered by tallgrass prairie, which supported a diverse array of plant and animal species, including grasses, wildflowers, and prairie wildlife.

Today, much of the county’s land has been converted to agricultural use, with crops such as corn, soybeans, and wheat being the most common. However, there are still pockets of natural habitat remaining, particularly along rivers and streams, where native plant species such as oaks, maples, and hickories can be found.

Wetlands and marshes are important ecosystems in DeKalb County, providing habitat for waterfowl, migratory birds, and other wildlife. These habitats also serve as natural buffers against flooding and erosion, as well as providing recreational opportunities for outdoor enthusiasts.

Human Impact and Development:

Throughout its history, DeKalb County has been shaped by human activity, from early Native American settlements to European colonization and modern development. The county’s fertile soils and abundant water resources attracted settlers to the region, leading to the establishment of farming communities, trading posts, and small towns.

Today, DeKalb County is primarily rural, with agriculture being the dominant industry. The county is known for its productive farmland, which supports a variety of crops and livestock, as well as agribusinesses and food processing facilities.

In addition to agriculture, education, healthcare, and manufacturing are also important industries in DeKalb County, with institutions such as Northern Illinois University and Kishwaukee College serving as major employers and economic drivers.

The county’s towns and communities offer a mix of modern amenities and historic charm, with shops, restaurants, and cultural attractions that reflect the region’s rich heritage.

In conclusion, DeKalb County, Illinois, offers a blend of natural beauty, agricultural heritage, and small-town charm. From its fertile farmland to its scenic rivers and lakes, the county provides residents and visitors alike with an opportunity to experience the beauty and tranquility of the Illinois countryside. As stewards of this diverse landscape, it is essential to promote responsible development and ensure the long-term sustainability of DeKalb County’s natural resources and quality of life for future generations.