The Central Illionis Chapter covers the counties of Sangamon, Chrisitan, Macon, De Witt, Logan, and Menard.

Cook County is the second most populous county in the United States after Los Angeles County. The county has 5,294,664 residents, which is 43.3% of all Illinois residents. Cook County's population is larger than that of 29 individual U.S. states and the combined populations of the seven smallest US states.  There are over 130 incorporated municipalities in Cook County, the largest of which is the county seat, Chicago, which makes up approximately 54% of the population of the county. The county is divided into 30 different townships. Geographically the county is the fifth largest in Illinois by land area and shares the state's Lake Michigan shoreline with Lake County.

Cook County is a county in the U.S. state of Illinois. It is the second most populous county in the United States after Los Angeles County. The county has 5,294,664 residents,[1] which is 43.3% of all Illinois residents. Cook County's population is larger than that of 29 individual U.S. states and the combined populations of the seven smallest US states. There are over 130 incorporated municipalities in Cook County, the largest of which is the county seat, Chicago, which makes up approximately 54% of the population of the county. The county is divided into 30 different townships. Geographically the county is the fifth largest in Illinois by land area and shares the state's Lake Michigan shoreline with Lake County.

DuPage County is a county located in the U.S. state of Illinois. Its county seat is the city of Wheaton. This county is part of the Chicago metropolitan area. The population estimate by the U.S. Census Bureau for 2008 is 930,528, making it the second most populous county in Illinois after Cook County, which borders it to the north and east; the two counties account for half of the state's population. The county is divided into nine different townships: Addison, Bloomingdale, Downers Grove, Lisle, Milton, Naperville, Wayne, Winfield and York. The majority of DuPage County is in the 630 and 331 area codes. However, the areas of the county that are in the city of Chicago are in area code 773, primarily part of O'Hare International Airport.

Long known as one of the nation's wealthiest counties, DuPage County has transformed itself from a primarily agricultural economy to one rich in many different types of commerce. Today, DuPage County has a per capita income which is the highest in the state. DuPage County's per capita income is also the highest in the midwest; nineteen of the county's towns have average household incomes of over $100,000.

The most populous municipality within DuPage County is Naperville. The next largest communities are Wheaton and Downers Grove. A small portion of the City of Chicago is located within the county limits; however, this area is primarily commercial and as of recent census estimates, has only 230 residents.

Kane County is a county located in the U.S. state of Illinois. In 2000, the population of the county was 404,119. The population estimate by the U.S. Census Bureau for 2008 is 507,579. This county is part of the Chicago Metropolitan Area. Its county seat is Geneva,  and its largest city is Aurora.

Kendall County is a small, but rapidly growing county that has the majority of its population in the north and east, and along the Fox River (the only river in the county) which runs through the northwestern section of the county. Many new subdivisions have been constructed in this county, which has produced considerable population growth. Southern Kendall still remains largely agricultural. Kendall County has two primary ranges of low-lying hills formed by what is known as an end moraine. Ransom, the more predominant of the two moraines, runs through the west and north-central part of the county. This moraine has created elevations of over 800 feet (240 m), in contrast to elevations in southern Kendall County that drop to the lower 500 feet (150 m) range. Minooka, the other major end moraine ridge in Kendall County, runs along its entire eastern border with Will County. The two moraines intersect at almost a right angle in the township of Oswego. The only designated state park in the county is Silver Springs State Park.

Lake County is the farthest north-east county in the U.S. state of Illinois. A 2006 census estimated the population was 713,076. Its county seat is Waukegan, Illinois. According to the 2000 United States Census, Lake County is the 31st richest county by per-capita income. The county is part of the Chicago metropolitan area. Its lakefront communities, along with some in Cook County, are part of an area known as the North Shore.

Originally part of McHenry County, the townships comprising Lake County were carved out into a separate county in 1839.

Lake County is also the location of Naval Station Great Lakes, which is the United States Navy's Headquarters Command for training, and their only recruit training center, located in the city of North Chicago.

Sauk Valley is an area that consists of Lee, Whiteside, Carroll, Ogle, and Bureau Counties.

The Southern Chapter covers the counties of Saline, Hamilton, White, Gallatin, Hardin and Pope.

Will County is a county located in the northern part of the U.S. state of Illinois. This county is part of the Chicago metropolitan area. As of 2000, the population was 502,266. In 2007, the estimated population was 673,586, making it one of the fastest growing counties in the United States. The county seat of Will County is Joliet, Illinois. The portion of Will County around Joliet uses the 815 and 779 area codes, 630 and 331 area code for far northern Will County, and 708 area code for eastern Will County.

Winnebago County is a county located in the U.S. state of Illinois. As of 2000, the population was 278,418. Its county seat is Rockford, Illinois. Winnebago County is part of the Rockford, Illinois, Metropolitan Statistical Area.