The Vasculum: The North County Journal of Science and History. Vol. 10 No. 1. Pg. 29. Published 1923.
Toponymic place-names are so frequent locally that it is not surprising to find a great many imitations, accidental and simulatory. Wherever there is an unaccented medial syllable the process of assimilation is likely to, came into play, almost inevitably where the syllable in question contains an “n”* An excellent example is HalIington, formerly Halidene. A remarkable instance is Follingsby which in 1140 was written Foletesbi-representing most probably Fulwihtes-bige, a place of baptism.
I am unsure of the validity of assuming Follingsby as representing Fulwihts-bige. Having seen the supposingly original charter from the Bishop of Duham to Thorald which was hundreds of acres of marsh land, Follongsby mentioned as a villiage and later 3 farms that were eventually sold off, to my mind it is unlikley it was named as a place of baptism.
This is just my personal opinion. There is no actual reason Thorald could not have named it as such. This would be easy to accept and call off the search for the origins of the name Follongsby. But, the location of Follongsby, the type of land, and its habitation status just build a different reasoning. It seems more likley that Thorald was building a source for finances and goods as a land owner or lord.
It is interesting that there a various reasonings for the name among as many histories. This tells me there (so far) is not a recorded meaning and reasoning behind the name. Rather, we are left to figure is out based on other evidences.