In the far lower left hand corner is New Amsterdam. Zoom in there and you can see that Bonnema owns the area around the town, but right up river, Sjoerd’s place (now in the Van Loon Floodplain Forest State Natural Area). Wish we had know this when we were going often so we could explore.
Scan around the map and you will see other familiar names.
Below is satellite photo with an arrow pointing to location of Sjoerd’s property. Given flooding, likely no evidence. Perhaps nothing was even ever built there.