The U.S. State of Illinois currently has 47 statistical areas that have been delineated by the Office of Management and Budget (OMB). On July 21, 2023, the OMB delineated 14 combined statistical areas, 12 metropolitan statistical areas, and 21 micropolitan statistical areas in Illinois.[1] As of 2023, the largest of these is the Chicago-Naperville, IL-IN-WI CSA, comprising the area around Illinois' largest city, Chicago.
The Office of Management and Budget (OMB) has designated more than 1,000 statistical areas for the United States and Puerto Rico.[2] These statistical areas are important geographic delineations of population clusters used by the OMB, the United States Census Bureau, planning organizations, and federal, state, and local government entities.
The OMB defines a core-based statistical area (commonly referred to as a CBSA) as the county or counties (or county-equivalents) surrounding at least one densely-settled core of at least 10,000 population,[2] "plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties with the counties containing the core".[2] The OMB further divides core-based statistical areas based on population into metropolitan statistical areas (MSAs) for those with at least 50,000 and micropolitan statistical areas (μSAs) for those with 10,000 to 49,999 people.[2]
The OMB defines a combined statistical area (CSA) as two or more adjacent core-based statistical areas where the employment interchange rate (% commuting from A to B plus % commuting from B to A) is at least 15%.[2] The primary statistical areas (PSAs) include all combined statistical areas and any core-based statistical area that is not a constituent of a combined statistical area.
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