My mother uses the pronunciation woish or worsh for wash, feesh for fish, and deleecious for delicious. What accent or dialect is this considered? She has lived her entire life in central Illinois.
According to a map based on the Atlas of North American English, central Illinois is unevenly apportioned into areas dominated by two major American dialects: Inland North, which accounts for the northern third of the state plus a long finger of territory called the St. Louis Corridor that extends in a line from Chicago and Gary (Indiana) through Bloomington (Illinois) and Springfield (Illinois) all the way to St. Louis (Missouri); and Central Midland, which includes parts of west-central Illinois from Peoria to Quincy to Jacksonville, and east-central and southern Illinois from Champaign and Danville to Hillsboro, Bellville, and Murphysboro.
The map also shows (with a solid purple line) the split between areas where natives pronouns pen identically to pin (with a short i sound)—generally north of the line—and areas where the two words are pronounced differently; the demarcation line for that split is not the same as the one for Inland North versus Central Midland.
Researchers at the University of Pennsylvania have produced a somewhat different (and less detailed) map that divides Illinois into three regions—Inland North, North Midland, and South Midland—with the area near St. Louis treated as a unique fourth area.
As for the poster's question about what dialect uses woish or worsh for wash, Merriam Webster's Eleventh Collegiate Dictionary (2003) reports that the pronunciations 'worsh (with a dot over the o that my computer's special character set won't let me replicate) and 'wärsh for wash are "chiefly Midland." I have no information on the pronunciations feesh and deleecious.
For a highly anecdotal series of posts about the pronunciation "warsh" (or "woish") for wash, see the responses to the question "Warsh?" at alphaDicitionary.com. Among respondents who bothered to identify where they lived, areas cited as using the pronunciation "warsh" or "worsh" include West Virginia (two instances), northern West Virginia, southwestern Pennsylvania (two), eastern Kentucky, southeastern Tennessee, western North Carolina, Ohio River Valley (two), Missouri (three), Iowa (two), Wisconsin, south Texas (two), central Texas, east Texas (two), north Texas (two), "rural" Texas, "rural" Florida, Oregon, central Washington, Baltimore (Maryland) and New Orleans (Louisiana); areas cited as using "woish" include Iowa and Wisconsin.
By way of emphasizing the evidentiary limits of such anecdotal reports, I note (counter-anecdotally) that I spent many years of my life in cities in south, east, and central Texas, and very rarely heard anyone say "warsh" or "worsh."
My mother claims to have said 'warsh' when she was younger. After getting a degree for speech therapy, she lost her accent. She no longer speaks that way, although sometimes she still says 'feesh' for 'fish' and 'cooshion' for 'cushion'.
She was born and raised in Central Indiana. But a generation before that, her family was in Southern Indiana. And some generations further back they were in Kentucky, Tennessee, North Carolina, and West Virginia. I've assumed that this was a dialectical trace from the Upper South.
My brothers and I spent most of our early life in the Midwest. This included a factory town on the edge of Appalachian Ohio, in a Jewish suburb of Chicago, and in a college town in Central-Eastern Iowa.
None of us have ever said 'warsh'. Other than my mother's family, I've rarely heard it spoken that way in most of the Midwest. It's even more rare among young Midwesterners. I have some cousins in Indiana and not a single one of them would ever say 'warsh'.