Route 9 started operating in 1974 as a replacement for other various lines that served Baltimore's York Road corridor north of Towson; historically, all portions of York Road Towson and southward were served by the no.
The Route 9 service commenced in 1974, replacing various routes that had previously served the York Road corridor north of Towson. It has since been responsible for covering the entire stretch of York Road from Towson down to the south.