The primary function of a regional council is to study the needs and conditions of a region and to develop strategies which enhance the region's communities. Regional councils are voluntary multi-service entities formed under Illinois law by counties and municipalities to serve local government planning needs.

There are currently fourteen multi-county regional councils and about the same number of single-county councils in Illinois having at least one full-time staff person. Half of the multi-county councils and all of the single county "regional planning commissions" were established under Chapter 55 (Counties) of the Illinois Compiled Statutes. Another three were established under Chapter 50 (Local Government): North Central Illinois Council of Governments (Princeton); Two Rivers Regional Council of Public Officials (Quincy); and Western Illinois Regional Council (Macomb).

The differences in the provisions of Chapter 55 and Chapter 50 have little practical significance. Chapter 55 calls upon "regional planning commissions" to make a plan, to prepare zoning and building codes, and to make investigations and gather statistics. Adopted plans are advisory in nature. Funding is also voluntary. Chapter 50 calls upon "regional councils" to study problems common to members, promote cooperation and coordination, and make recommendations. Their powers are also advisory and their funding voluntary.

Regional Council Act (50 ILCS 10/)
Regional Planning Commission Act (50 ILCS 15/)
Counties Code - Regional Planning (55 ILCS 5/)

The Chicago Metropolitan Agency for Planning (CMAP) and the Southwestern Illinois Metropolitan and Regional Planning Commission each have their own separate state enabling acts, while the East-West Gateway Coordinating Council and Bi-State Regional Commission both resulted from interstate agreements or compacts. None of these specially created agencies has powers significantly different from those created under the general provisions of Chapter 55 and Chapter 50.

CMAP Regional Planning Act (70 ILCS 1707/)
Southwestern Illinois Metropolitan and Regional Planning Act (70 ILCS 1710/)

The terms "council of government", "regional council" and "regional planning commission" are overlapping but not synonymous. For example, not all councils of government (COGs) are "regional," – they do not always cover an entire metropolitan area or a rural, multi-county region. Some councils serve only one county within a metropolitan region or only portions of a county or counties. Councils of this type are found in suburban northeastern Illinois. These may be established as not-for-profit organizations – 501(c)(3) – or under state statutes providing for intergovernmental cooperation. Sub-regional COGs having full-time staff include the Barrington Area Council of Governments, DuPage Mayors and Managers Conference, Northwest Municipal Conference, South Suburban Mayors and Managers Association, and West Central Municipal Conference.

Single-county regional councils functioning as councils of government have been created by joint agreement of two or more units of government. These agencies have board representation and financial support shared between their county and municipal governments. Such agencies include the Boone-Belvidere Regional Planning Commission, Champaign County Regional Planning Commission, McLean County Regional Planning Commission, and Springfield-Sangamon County Regional Planning Commission.

Most single-county regional commissions are tied more exclusively to a single parent county government. Commission members are appointed by the county board chair and staff work is performed by a county planning department. Membership on these single-county commissions may, however, include municipal and private sector representatives as well as county officials. Examples of this type of single-county "regional planning commission" are found in Coles, DeWitt, Kankakee and Macon counties. Within the six-county northeastern Illinois area, which is under the jurisdiction of the Chicago Metropolitan Agency for Planning, five "regional planning commissions" with full-time staff coexist with CMAP: DuPage, Kane, Lake, McHenry and Will counties. Cook County has a planning department but do not have a commission.

Some single-county regional planning commissions also contract with municipalities outside their county boundaries to provide planning services in those areas not covered by another planning commission. Several multi-county planning commissions also offer contractual services to areas otherwise unserved by a planning commission. This extension of services to these otherwise unserved areas provides statewide coverage by some type of regional planning organization.