$20k on $500k is 4% annually, which is really high. I'm not seeing any Chicago neighborhoods that are this high (looks like a max of maybe 2%) but perhaps I'm missing something about how Chicago works?
Cook County has senior exemptions, senior freeze exemptions, and long-time homeowner freeze exemptions. They don't push any responsible homeowner into poverty. They also have a website so you can look up exactly what your neighbor's assessed value and annual tax is. There is no need to guess.