Trying to trace family branches in Malew, I found the List of residents in Castletown about 1757 to be useful (from Francis Coakley's web site). The list includes 210 houses covering 894 people. The 1757 Clergy Census lists 915 - with the difference being explained by the absence of soldiers in the garrison.

Has anyone any idea if this is likely to be the total population of Castletown at that time?