Emma,
I do know where they were! As a child I used to visit my grandparents who lived in Ightham. My cousins and I used to walk from Ightham to Crouch, the mill was not far from Crouch, about Claygates Cross.
I had an Uncle who used to work there too. Am not sure when it closed and would be guessing. I am pretty sure it was still operational in the 1950's. Hope that is of some help. Ightham, Crouch and Claygates Cross can be seen on most 3m to inch maps.
Sheila