I agree that they've exhausted US Census searches. There are still some remaining research avenues.

You should look for a book about History of Shelby County, Indiana on Heritage Quest. You might be lucky and find a bio in the typical prominent citizens of the county that are in those type of books. http://www.rootsweb.ancestry.com/~inshelby/

You should search the Delaware probate records.
http://archives.delaware.gov/collections/probate.shtml You'll have to read all the records in a time window that could match your John's father death.

There is a series of books called Calendar of Wills where you might find your John. http://books.google.com/books?id=g-VQ24f01gwC&pg=PA40&am...

There is also a series of books with transcribed bible records.

The Delaware Historical Society ought to have the wills and bible books.

DNA tests may help. It won't make the connection for you but you can see over your brickwall. Unfortunately, the Family Tree DNA has only 2 Derickson in the Derickson project so not worth pursuing unless you are patient for others to join and match.

The Delaware Historical Society is a good place. Good Luck in October.
http://www.hsd.org/library.htm