I'm curious percentage wise how many people are having to file returns with their city or county. I've lived in two states (Alabama and Georgia) and even in a city with an "income tax" at the city level and have only ever had to file federal and state taxes

In Alabama the county and city I lived and worked in both had what they deem occupational taxes which are effectively an payroll tax, but there was no system of exemptions or refunds, it operated as a payroll tax only. My employer had to file the taxes, not me

I suspect the vast majority of people in the US only ever file state and federal returns, although a lot of people live in small states or along state borders so a lot probably have to file two state returns