Keri has led the Trust through the clubs dark days whereby administration looked certain.
He has played an active part in the rebuilding of Notts County from near ruin.
Keri finishes his role as Chair as the longest ever servant after being appointed on 21 October 2004.
He admitted that his decision has not been taken lightly and it has been thought about for some time.
Following the death of Notts legend Haydn Green, Usherwood has always had the intention to step down from his role.
But his departure was put on hold out of respect for the man who ultimately stepped in to save the club.
NCM would like to thank Keri for all his hard work and wish him all the best for the future.
Trust board member David Hindley will take over with immediate effect until the clubs next AGM.
Visit the official Notts County website for Usherwood's full statement.