I seem to remember from many years back being told that at the time of the Foster Education act in 1870 (which brought in compulsory elementary eduction for all in the UK) about 70% of the UK population could read and write at least to some degree.

It also seems that there was a pretty substantial level of musical literacy as well. After all how could all the manuscript tune books have been produced otherwise? The 19th century also saw the birth of most of our brass bands, choral societies and male voice choirs. All of these required a degree of musical literacy and before that the parish churches maintained bands and choirs to provide music for the services.