While going through the photographs we have in the McKinley Presidential collection I found three that were taken in Plattsburg, New York. I looked at the first two photographs and determined they could have been taken almost anywhere. The third one, above, featured full views of two buildings, that President McKinley and his party passed.
Going to Google Maps, I searched for the city of Plattsburg, NY. The program offers an aerial view in the maps portion, and a satellite view in Google Earth. The program also offers a street view where possible. I went to the street view and it took me to this location, or a location with buildings very similar to the buildings in the above photograph.
Next, I found and called Clinton County Historical Association and Museum where I spoke to Julie, their historian. She told me the area where President McKinley and Vice-President Hobart were in this 1899 photograph was government land from 1814 to 1994. The government purchased this land after the battle of Plattsburg in 1814, and the Air Force last occupied this land in 1994. The land and the buildings that occupy it now belong to the city, and are privately owned.