Hi Amanda,
Re the entry in the 1841 Census for William P. Morley, I think you will find that it states:-
Silk Throwster, co-partner with J P Morley. Employing 24 Men, 150 Women & 80 Children - 254.
The entry for John P. Morley has a similar entry:- Silk Throwster, co-partner with W P Morley.
The extract from the book, The Old Derby Silk Mill & Its Rivals by Harry Butterton states:-
"The diversity in location matched the expansion of the town southwards during these years
with the sale at long last of the Castlefields and Normanton estates. Breaking the stranglehold of the feudal past on land to provide new sites for worker's housing. As an illustration of this development, no less than four silk mills sprang up along the Normanton Road, three of them headed by members of the Morley family.
Taking the 1851 Census and the book entry, you are looking for a Mill named "Depot Mill", Normanton Road, Derby in the Parish of St. Werburgh.
In the book "The history of the County of Derby~" by Stephen Glover 1829, it lists Messrs. Ambrose
Moore at the Depot Mill - so it looks as if the Morley Brothers took over a going concern.
You are unlikely to find any workers records etc., however you may be lucky and find land/property
transactions you need to search A2A via the National Archives web site.
Spendlove.