Quite possibly the oldest stereoview I have – I’d put this one at no later than 1870. This may have even been taken during the Civil War, although I think you’d have been hard pressed to find Pennsylvania Avenue that empty during the war. The area around the White House was even more the center of government at that time than it is now (now federal agencies are spread throughout the town and into the suburbs). The State Department was across the street to the north, and the War department was the other side of the White House. But Washington was a much smaller town in those days, and when Congress was not in session, half the town was empty.
dcphotoartist 
Love the label! I often wonder about these architectural shots. There are so many from around this period where the human form is no where to be seen. Do you think they could have edited the people out?
No. The people were not edited out. Either the photo was taken at a moment when there were no people walking around, or the exposure was long enough that they did not record. This is a well-known phenomenon in early photography – one of the first ever Daguerreotypes shows a seemingly empty Parisian street except for a blurry image of a man getting his shoes shined. It was actually a very busy street, but the exposure was long enough (several minutes) that only the shoeshine customer stood still long enough to record on the plate. Wet plate collodion, although much faster than daguerreotypy, still requires multiple seconds for a full daytime exposure. Given that this is the facade of the Treasury building facing the White House, I would have expected at least some sentries to show up if it were the case that the people were missing due to long exposure.