Collar Counties of the Chicago Metro: DuPage, Lake, Kane, Will, and McHenry

The five collar counties — DuPage, Lake, Kane, Will, and McHenry — form the suburban ring surrounding Cook County in the Chicago metropolitan area. Together they account for a substantial portion of the region's population, economic output, and land area, each operating under its own elected county government while remaining functionally integrated into the broader metro through transportation networks, regional planning agencies, and intergovernmental agreements. Understanding how these counties are defined, governed, and differentiated is essential for anyone navigating services, land use decisions, or policy at the regional scale.

Definition and Scope

The term "collar counties" is a colloquial but institutionally recognized designation for the five Illinois counties that directly border Cook County: DuPage to the west, Lake to the north, Kane to the northwest, Will to the southwest, and McHenry to the northwest of Lake. The U.S. Office of Management and Budget (OMB) designates the broader Chicago–Naperville–Elgin metropolitan statistical area (MSA) to include all five collar counties alongside Cook County, making the combined region one of the largest MSAs in the United States by both population and geographic extent.

The Chicago Metropolitan Agency for Planning (CMAP) uses the same six-county footprint as its primary planning jurisdiction, producing long-range plans — including the ON TO 2050 regional plan — that treat the collar counties and Cook County as a single integrated system. For federal funding, census reporting, and regional transportation planning, the collar counties are therefore not peripheral but structurally central to how the metro functions.

Collectively, the five counties encompass roughly 3,650 square miles of land area. Will County alone covers approximately 837 square miles, making it the largest of the five by area. DuPage County, while the smallest geographically at approximately 334 square miles, is among the most densely developed.

How It Works

Each collar county operates as an independent unit of Illinois county government under the Illinois Constitution and the Illinois Counties Code (55 ILCS 5). All five counties use a county board structure rather than a county executive model, meaning an elected board of commissioners or supervisors holds both legislative and executive authority, though the specific board size and election structure differ by county.

The following breakdown identifies the primary governing structure and a key attribute for each collar county:

1. DuPage County — Governed by an 18-member County Board elected from 6 geographic districts; the county seat is Wheaton. DuPage is the second most populous county in Illinois, with a 2020 U.S. Census population of 932,877 (U.S. Census Bureau).
2. Lake County — Governed by a 21-member County Board; the county seat is Waukegan. Lake County borders Wisconsin to the north and Lake Michigan to the east, giving it a distinct geographic and regulatory context for shoreline and water management.
3. Kane County — Governed by a 24-member County Board; the county seat is Geneva. Kane County includes Aurora, Illinois's second-largest city by population.
4. Will County — Governed by a 26-member County Board; the county seat is Joliet. Will County recorded the fastest population growth among the five collar counties between 2000 and 2020, driven by southward suburban expansion from Cook County.
5. McHenry County — Governed by a 24-member County Board; the county seat is Woodstock. McHenry is the most rural of the five counties and includes significant agricultural land in its northern sections.

Each county independently administers property assessment, recording, circuit court operations, public health services, and sheriff's office functions — parallel but separate systems to those operated by Cook County.

Regional coordination occurs primarily through CMAP, the Regional Transportation Authority (RTA), and the Metropolitan Water Reclamation District, which extends its jurisdiction into portions of the collar counties. Metra commuter rail lines connect all five collar counties to Chicago's Loop, and Pace Suburban Bus operates fixed-route and paratransit services across the suburban ring.

Common Scenarios

The collar counties arise as a relevant geographic and administrative unit in a consistent set of real-world contexts:

• Residential relocation decisions: Property tax rates, school district boundaries, and zoning classifications differ substantially across the five counties. A parcel in Will County is assessed and taxed under Will County Assessor procedures entirely independent of Cook County's assessment methodology.
• Business permitting and licensing: A business operating in Naperville, which straddles DuPage and Will counties, may need to coordinate with two separate county health departments and building departments depending on the specific parcel location.
• Transportation planning: Metra's BNSF line, for example, runs from Chicago Union Station through DuPage County into Kane County, meaning capital project decisions involve CMAP, RTA, and at minimum two county governments.
• Regional healthcare and public health: Each collar county maintains its own public health department with independent authority over food inspections, communicable disease reporting, and environmental health permits. During state-declared public health emergencies, these five departments operate under the Illinois Department of Public Health (IDPH) alongside but separate from the Cook County Department of Public Health.
• Electoral and judicial administration: Circuit courts in the collar counties belong to their respective Illinois judicial circuits — DuPage County is the 18th Circuit, Lake is the 19th, Kane is the 16th, Will is the 12th, and McHenry is the 22nd — each independent of the Cook County Circuit Court.

Decision Boundaries

The collar county framework creates meaningful administrative and legal boundaries that affect how residents, businesses, and planners must approach cross-county matters.

Collar counties versus Cook County: Cook County operates under a home-rule county government structure with a separately elected County Board President exercising executive authority, a model not used by any of the five collar counties. Cook County's property tax system also uses a triennial reassessment cycle administered by the Cook County Assessor, while each collar county follows its own assessment schedule under the Illinois Department of Revenue (IDOR) guidelines — typically a four-year reassessment cycle for townships within those counties.

Collar counties versus Chicago: The City of Chicago's home-rule authority, derived from the Illinois Constitution (Article VII, §6), applies exclusively within Chicago's municipal boundaries. Chicago ordinances governing building codes, business licenses, or zoning do not extend into the collar counties. Entities subject to Chicago's regulatory framework — such as those tracked through Chicago's business licensing system or the Chicago Department of Buildings — have no corresponding obligation in the collar counties absent a separate municipal or county ordinance.

Intra-collar variation: The five counties are not uniform in policy or capacity. Lake County's proximity to Wisconsin creates regulatory adjacency on issues such as groundwater compacts. Will County's rapid growth has produced a larger capital improvement backlog than McHenry County, which faces different fiscal pressures related to lower population density. Kane County's bifurcated urban-rural character — with Aurora's dense urban core alongside far western agricultural townships — produces land use conflicts that DuPage County, which is almost entirely built out, does not encounter at the same scale.

Scope and coverage limitations: This page addresses the five collar counties as a collective administrative category within the Chicago metropolitan area. It does not address Kendall County, which the OMB includes in the Chicago MSA but which is not traditionally counted among the five collar counties. DeKalb and Grundy counties, which border collar counties but fall outside the core MSA definition, are also outside the scope of this page. For a broader orientation to Chicago-area governance, the site index provides navigation to individual county pages and the full range of regional institutional topics covered in this reference.

References

• U.S. Office of Management and Budget — Metropolitan Statistical Area Definitions
• Chicago Metropolitan Agency for Planning (CMAP) — ON TO 2050 Regional Plan
• Illinois General Assembly — Illinois Counties Code, 55 ILCS 5
• Illinois Constitution, Article VII — Local Government
• U.S. Census Bureau — 2020 Decennial Census, Illinois County Population Data
• Illinois Department of Public Health (IDPH)
• Illinois Department of Revenue — Property Tax Division
• Regional Transportation Authority (RTA)
• Metropolitan Water Reclamation District of Greater Chicago