Here are the directions, as provided to me: "The duck turned up in an apartment complex called The Arbors of Mount Vernon. They are on Yauger Rd., just off of 36 at the east end of town. I hope some folks can find it. As I said, we are close to the Kokosing River, and about 20 minutes south of Knox lake." A map is below:
Following is a note from the observer: "Last night [Wednesday, June 20] as I was sitting on my patio, a duck flew over the roof of the apartment, and then it landed on the roof. I had never seen a duck land on a roof. It stood very upright, had a black belly, a chestnut breast, and sent up a long sing-song cry. I immediately got my iPad to identify it. It turned out to be a black bellied whistling duck! The call on the website was identical. The duck flew away, but as I played the call, it returned and landed again on the roof, whistling a reply. I took a few pictures and a video, but it was so high that the quality is poor. I did get the call on the video though."
I'm sure we'll be seeing yet more of these wonderful gooselike whistling-ducks, and good luck with the chase should you try and find this Knox County bird.