Ask Mr. Smarty Plants

If you are referring to Urtica dioica (Stinging nettle), it is shown in Turner et al. Atlas of the Vascular Plants of Texas as occurring in Texas only in Wheeler County in the Panhandle.  Urtica chamaedryoides (Heartleaf nettle), however, does occur in Travis County.  It is also called "stinging nettle" by some and, indeed, Green Deane on the Eat the Weeds website calls it "the nettle that stings the worst".  Unfortunately, I don't have first hand knowledge about where it might occur at all and certainly not where plants that haven't been exposed to pesticides or exhaust from automobiles could be found.  I think your best bet for finding such stinging nettles is by contacting fellow wild food foragers.   In the Austin area there is the Texas Wild Plant and Food Foragers.  On Facebook you can find the Wild Food and Foraging Austin page.  You might also try contacting someone in the Austin Chapter of the Native Plant Society of Texas.

For foraging in Texas there is Foraging Texas:  Merriwether's Guide to Edible Wild Plants of Texas and the Southwest and Wild Edible Plants of Texas websites.  And, if you don't already know it, there is the 2013 book by Delena Tull, Edible and Useful Plants of the Southwest:  Texas, Mexico and Arizona available in the Wildflower Center store.  This is the revised version of her 2009 publication Edible and Useful Plants of Texas and the Southwest.

Here are three different discussions about edible native plants in the Austin area by another Mr. Smarty Plants contributor that you may find interesting:  discussion #1, discussion #2 and discussion #3.