I had already spotted art covers near Theo's Chocolate Factory in Fremont (this one by Betsy Best-Spadaro, titled Water Ring)
and by the Recovery Cafe near Denny Way.
On Jaunary 30, 2013, I spotted these two manhole covers and a few utility covers outside the Waterfall Garden at 2nd and Main.
Walking north on 2nd, I spotted two more covers and then two more Nathan Jackson covers at 3rd and Columbia and 2nd and Seneca.
According to http://www.kpluwonders.org/content/why-did-seattle-turn-manhole-covers-works-art, there are 115 covers and
There is no list or map of where they are. The covers are stored in utility warehouses and used or moved around as needed, just like the regular manhole covers.
I wonder if they will be there when I return to these locations. So far, I have spotted about 23 of the 115 covers (I don't think the Home Plate cover is included in the 115 count); on April 26, 2014, I finally spotted two of the nine Edward Garth untitled covers (see picture below). Nathan Jackson's Native American design seems to be the most common (I've seen 8 and I think there are 32) followed by City Light, City Bright (I've spotted 7). I've only seen three Water Ring (I don't know how many exist) and three Seattle Grid (I think there are 19 of these).
I've read that there are new hatch covers, named The Web, in the redeveloped South Lake Union area. I returned to the area on August 24, 2016 and spotted two, one at Valley and Westlake and the other at Mercer and Westlake.
The very first art cover I spotted was in an intersection but almost every other one I have spotted has been on the sidewalk. I don't know if it's because I'm walking on the sidewalk making the ones under my feet more obvious or if the city is placing most of the covers on the sidewalk.