You are not imagining, there has been a catastrophic decline in the Blue Jay population and their closest relative, the Common Crow.
I did a little searching online, the culprit is the West Nile Virus.
West Nile Virus is most seriously impacting the following avian species: Crow, Black-Capped Chickadee, Tufted Titmouse, Blue Jay, Ring-Billed Gull, Common Grackle, House Finch, and House Sparrow.
Other species in decline are Northern Cardinals, owls, all species of raptors, and Gray Catbird.
The virus is new to the Western Hemisphere, and will decimate many species of birds. Those few that survive will be genetically resistant, and pass on their genes, while those which are not immune will not pass on their genes. So in a few dozen bird generations, there will be a new population that is resistant to the virus. Not in our lifetime, but this is an example of evolution in action.