After a federally declared disaster, the IRS routinely postpones filing and payment deadlines for taxpayers whose address of record is in the covered counties. The relief is automatic. You do not apply for it, and you do not file an extension to get it.
What moves
Typically every filing and payment deadline that falls inside the relief window moves to a single new date, often several months out. That usually includes individual and business returns, estimated payments, and payroll deposits due in the window. Interest and penalties are waived for the postponed period.
What does not move
Deadlines that fell before the disaster date. A return that was already late stays late. And relief follows the address the IRS has on file, so if you moved and did not update it, the relief may not attach to you.
How to check
The IRS posts every declaration on its disaster relief page, by state, with the covered counties and the new date. If your county is listed, the new date is your date. If you are outside the area but your records or preparer are inside it, you can call the IRS disaster hotline and ask for the same relief.
Common mistake
Filing Form 4868 during a relief period because you are nervous. The extension runs from the original April date, so it can end before the disaster relief date does. If the relief already covers you, let it.