Removed from service due to cost to maintain and operate and supposedly replaced by satellite coverage.
One or two came back briefly for NASA test flights. There are rumors of a possible SR-72 being developed as technology moves forward and satellites are not always the best answer in all cases.
Wasn't the SR-71 given up for some nuclear treaty with USSR? I know that the engines of several of them were destroyed. I don't know if there is one in operational status yet. There was one at FT Snelling Museum in St Paul, MN as a static display. The classified items were taken out and it was not flyable.