This is an interesting question, almost a "trick" question, and one that I can only assume the answer due to the eyewitness account of William Shepherd. With this in mind, we can be very, very specific about the place! Let me explain.
"Eyewitness at the Triangle" was published in the Milwaukee Journal, March 27, 1911; however, this says nothing about the "where" of where it was "written" and happened. In reality, the story was "dictated" and not "written." The very famous "Triangle Shirtwaist Factory Fire" happened only a couple of days before. Shepherd's article is about that fire which happened in New York City on the corner of Washington and Greene in Lower Manhattan. It was Shepherd's instinct that told him to pick up a phone and report about the smoke he saw coming from the building. He called the United Press. The United Press then sent the story (via the telegraph at the time) all over the country. Therefore, we can assume that the original account of "Eyewitness at the Triangle" was written in New York City, and exactly on the corner of Greene and Washington in Manhattan.
I was walking through Washington Square when a puff of smoke issuing from the factory building caught my eye. I reached the building before the alarm was turned in. I saw every feature of the tragedy visible from outside the building. I learned a new sound—a more horrible sound than description can picture. It was the thud of a speeding, living body on a stone sidewalk.
That being said, what Shepherd witnessed was a grotesque scene of death with young ladies who worked for the Shirtwaist Company jumping to their deaths as flames licked their faces.
Thud—dead, thud—dead, thud—dead, thud—dead. Sixty-two thud—deads. I call them that, because the sound and the thought of death came to me each time, at the same instant. There was plenty of chance to watch them as they came down. The height was eighty feet. The first ten thud—deads shocked me. I looked up—saw that there were scores of girls at the windows. The flames from the floor below were beating in their faces.
The firemen's ladders didn't reach the three floors that the company occupied. The nets to catch the women weren't strong enough. The nets broke whenever more than one person tried to jump at the same time. Hundreds of young ladies died, and the nation was in shock due to Shepherd's story. The fire codes of New York City were lax up until that point. This tragedy changed those codes forever. It proved that governmental control in regards to safety was very important in a big city like New York.