I noticed that you mentioned De Smet, SD, in your posting.
I'm actually more focused on the Whiting line; specifically Amos Whiting, who homesteaded near De Smet. His mother was a Wilmarth.
I don't have much information on the Wilmarths, but you can check out what I do have, which is on my web page. The address is http://users.ecenet.com/wdcopper/http://users.ecenet.com/wdcopper/. Go to Wilmarth on the Surname drop down menu and you will find Rebecca Wilmarth who married Timothy Newell Whiting.
Please let me know if anything seems to connect to your information.