Start with the answer
Plant and System Operators, All Other pay in Illinois and Massachusetts
The May 2025 BLS OEWS median for Plant and System Operators, All Other is $77,780 per year in Illinois. It is $120,660 per year in Massachusetts. Illinois is 35.5% below Massachusetts on the published median.
Both rows use SOC 51-8099 and the same annual wage metric. Median means the middle of each area's published wage spread. It is not one worker's pay. The larger median is not proof that one place gives a better job or a better result. It is one wage fact from one source period.
BLS lists 230 wage and salary jobs in Illinois and 40 in Massachusetts. Those are survey job counts, not open posts. Read pay, job scale, local share, and price level as separate facts before you make a choice.
Evidence: bls-oews-may-2025 · Rule: same-soc-same-metric-pair · nominal-median-gap · employment-not-openings