While Plymouth and Whitemarsh Townships have rising resident populations (there was lots of room to build new housing), Conshohocken and West Conshohocken’s populations have been stagnant since 1990. What is curious about Conshohocken particularly is that the addition of the condo and apartment buildings hasn’t added to the population. This is probably due to the housing stock in the neighborhoods now being home for smaller families and even individuals.
Conshohoken’s population peaked between 1920 and 1970 when it was between 10,000 to 11,000. Today’s population is comparable to that of 1910 to 1920. You can view the specific numbers here.
See the data since 1990 from the US Census below: