Call a local branch and find out which ones.

Also, your local news stations usually list them.

There are no Post Offices in Pennsylvania open late tonight, according to the evening news.

No post office within 70 miles or more are open. I think that I heard that there were fewer and fewer people using the service as more people e-filed.

I have only seen it at big city post offices. And I have always thought it stupid....everyone knows that they have till April 15, and if they wait until the last minute, we should not have to cater to them.

Don't worry.

If you're not - you can file an extension here: https://turbotax.intuit.com/irs-tax-extensions/ (You don't have to own their software - but you can beat the deadline without a trip to the post office - it avoids the penalties for failing to file the return, and filing a couple of days late with a payment would be a miniscule fine)

If you really want to find a post office - try for one near an airport. The one near the Cleveland airport used to be open 24 hours a day - it has cut back some but still has very extended hours compared to most.