As Ginny pointed out, the ATC has a lot of good info on A.T. use. Laurie, as the ATC’s “Information Specialist”, is a great source of info for more detailed stats than are recorded on the website.
Although the thru-hiker numbers were consistently rising, I’m convinced that they spiked in the late 90’s and peaked in 2000 due to Bryson’s book - the one with the bear on the cover 
As for whether the trail is crowded these days… that’s a very relative question. There’s clearly more use than in '82 and you are not likely to have many days on the Trail without seeing anyone anymore.
However, if the NOBO hikers are like a long strung-out train, its definitely possible to find empty cars. I thru-hiked in '96 & '04, but also hiked more than half the trail in '01 & '06. On all four of those hikes I was able to find “voids” or gaps in the hikers & occasionally hike for two days or more without seeing a single thru-hiker. I would guess that in all that hiking, I had maybe 7 days total of not seeing a single human being - a fairly rare occasion…
I actually think its great that there are many more people to enjoy it and come away from the trail with a clearer perspective on life.
If you want a more solitary hike, just make sure to stay away from shelters & hostels & camp away from the trail.
freebird