This state's classification carries no date range for the species.
Not listed anywhere in the 2026-2027 Digest's exhaustive season-dates table or hunting timeline, confirming no current open season. Illinois' wild ruffed grouse population has been largely extirpated statewide since the early 1900s (habitat loss/fragmentation); secondary sources describe only small, non-established remnant/reintroduced pockets (e.g., a possible remnant/dispersal population in extreme northwestern IL, a small Pope County population traceable to 1950s-60s releases, and 1982-94 releases in Union/Alexander/western Jo Daviess counties 'not considered established'). Could not find a single IDNR statement citing an exact closure date — this conclusion is inferred from the species' total absence from current regs plus secondary population history; flagged for human review if a harder citation is needed.
Lower-confidence closure, flagged explicitly (mirrors the CA white-tailed ptarmigan judgment call from the prior Tier B batch): season has been closed statewide for decades due to population decline, and a fresh check 2026-08-19 (IDNR's own uplandgame.html page read directly, plus targeted search) found no mention of any ruffed-grouse monitoring, drumming-count survey, or IDNR grouse-specific page at all -- the most recent drumming-count data found in any pass dates to 2016, predating the closure. Not a documented confirmed-absence statement from IDNR itself, but the total absence of any current program reference across every source checked (an IDNR primary source, a dedicated search pass, and the Tier A registry's own prior pass) is the closest fit of the three buckets; worth a second look with different search terms or a direct IDNR wildlife-program inquiry.