Code Section 7508A grants an automatic 60-day extension to taxpayers living in federally-declared major disaster areas, for obligations that include filing federal tax returns and paying federal taxes.
The 60-day period begins with the first date specified in the disaster declaration, which I believe is February 11 (haven’t found it posted anywhere yet). That would be April 11 or thereabouts. But it ends 60 days after the “latest incident date” specified in the declaration. I don’t think we have reached that date yet, so it looks like Texas taxpayers in at least 77 counties will have some sort of extension.
IRS (technically, Treasury) can extend the date by up to a year.