Question

When is parking free downtown?

Street and meter parking rules in the US are set by local city governments. Therefore, whether parking is free downtown is specific to each city.

The general US free parking rules include free overnight parking after the meter hours end, which is usually from 8.00 pm to next day 8.00 am. In mid to small cities, Sundays are free all day. But in larger cities (like NYC, Chicago, San Francisco) often enforce Sunday meters in dense commercial districts. 

Similarly, parking is free downtown on major city holidays like Thanksgiving Day, Memorial Day, Labor Day, and Christmas. In addition, there is free parking for disabled card holders.  

Always check the street signs. Pay stations and street-sweeping signs take precedence over general city rules, and parking in a red zone or tow-away clearway is never free.