Illinois State Senate District Boundaries for 2024

Illinois state legislative district boundaries for the upper chamber (senate) as provided to the U.S. Census Bureau by May 31, 2024. This shapefile is part of the national TIGER/Line series, designed to stand alone or be combined for national coverage. The boundaries reflect the most current state-defined districts, though some areas may be assigned the 'ZZZ' code where districts were not fully defined.

Use Cases

• Analyze the spatial distribution and contiguity of Illinois State Legislative District Upper Chamber (SLDU) boundaries for redistricting research.
• Join demographic or election data using the unique three-character census code assigned to each SLDU for state-level political analysis.
• Map areas within Illinois assigned the 'ZZZ' code, indicating regions where the state participant did not define SLDUs to cover the entire state.
• Combine this Illinois SLDU shapefile with other state files from the TIGER/Line series to create a national map of upper chamber legislative districts.

Strengths

• Boundaries are sourced directly from state participants to the U.S. Census Bureau, ensuring official status.
• Data is part of the Topologically Integrated Geographic Encoding and Referencing (TIGER) System, designed as a seamless national file with no overlaps or gaps.
• Includes a unique three-character census code for each district, facilitating data linkage and analysis.

Limitations

• Some areas in Illinois are assigned the generic 'ZZZ' code because the state participant did not define SLDUs for the entire state, reducing completeness for those regions.
• The dataset does not cover the Island Areas (American Samoa, Guam, the Commonwealth of the Northern Mariana Islands, and the U.S. Virgin Islands).
• Boundary updates are periodic; this version reflects information provided by May 31, 2024, and may not capture later court-ordered changes in other states like Michigan.

Provenance

Source

U.S. Census Bureau, Department of Commerce

Collection Method

Extracted from the Master Address File / Topologically Integrated Geographic Encoding and Referencing (MAF/TIGER) System based on boundaries provided by state participants.

Time Range

Current as of the collection date; boundaries reflect information provided by states by May 31, 2024.

Freshness

Last updated 2025-12-24, with the next scheduled collection of boundaries in early 2026.

Geography

State of Illinois, USA.