Here is the list of every space telescope launched by different space agencies - List of space telescopes. Most of the listed telescopes are placed in Lower Earth Orbit (about 95% of them). It's probably not an ideal location to place a telescope because of many obvious reasons like our earth radiates a huge amount of infrared radiation; as said by professor Michael Merrifield -"Its like doing astronomy with all the lights switched on" .
Now here is the list of all objects placed at Lagrange points - List of objects at Lagrangian points. There are hardly 10 objects at these points. The lifespan of these objects are quite low, but surely there are many upcoming missions in these orbits, the most famous one being the James Webb Space Telescope:
The JWST will be placed on L2 Lagrange point. So clearly this will be the only orbit of choice for many future upcoming telescope missions. So finally concluding I have some questions-
Why are there so few Telescopes at the Lagrange Points despite having so many advantages? Is it a budget related issue, is it not feasible enough in a grand scale? There are/were some observatories at the Lagrange Points and we hardly heard about them - unlike the Hubble space telescope which is regarded as the most successful and most important man made creation by many. Will all future space telescopes be based at the Lagrange Points?