Last week's historical photo challenge was a tough one; there were plenty of incorrect answers before the correct one came in. The house pictured in the photo is set back in the woods off Goshen Road, as can be seen in the modern day photo.

The photo depicts Thomas Mill in Willistown Township, located across the street from Bartram's Bridge at the border of Willistown and Newtown townships—and Chester and Delaware counties, for that matter.

Today, an engraved stone at the driveway to the building reads "Thomas Mill Farm est. 1745."

According to a historical narrative (PDF) at the Library of Congress, which also supplied the photo, "Isaac Thomas built the mill in 1774 on land inherited from his father, Peter Thomas."

Kudos to Eric Lewis, who did some digging to come up with the correct answer:

I'll admit, this was a tough one. I believe it's the Thomas (Sager) Grist Mill, c. 1774. 6004 Goshen Rd in Willistown. Doesn't appear to be visible from the road. Using Bing Maps, winter shots to see through trees, it's the small building dead center: 

http://binged.it/XXMpH8 

You can see a connection to Crum Creek. It doesn't appear to be a "registered" building, so this might be private property. Might try a drive-by today.

His response was endorsed by commenter Its About Time. Plenty of other guesses came in, including spots in Charlestown and even General Warren Inne.

See more photos and links to a historical narrative of the property at the Library of Congress website.

Thanks to everyone who registered a guess!