I have read your post as well as the one you made about Ralph J. Nelson. I assume you posted here on the Corson County Board because Albert Nelson listed Corson as his place of birth on his WWI draft registration.
It appears that the family moved to Minnehaha County early on and that is where Ralph lived all his life.I am fairly certain he died in 2005. I have found his marriage record and an obituary for one of his children which gives the names of the remaining six children and his wife. Because these people are all alive I will email the information I have found to you
A website called findagravedotcom shows Albert and Agnes Nelson buried in Beaver Valley Lutheran Cemetery Valley Spring, Minnehaha County South Dakota. Ralph J. Nelson is buried in Zion Lutheren Cemetery Garretson Minnehaha County SD.
Let me know if you don't get the email with more information.
Hope that helps,