Census records and population tables
Some of the Scottish Post Office directories include population tables or summaries of the most recent local census.
These would usually give a list of individual places with their number of residents and record statistical changes compared to previous years.
In 'Leslie's directory for Perth and Perthshire' for 1891-1892, for example, you can read that Perthshire's population decreased by 3,225 between 1881 and 1891.