I'm installing a sub. pump, 240 volt 2-wire that pumps 250' to my pressure tank under the house. Where does the code require the disconnect to be located? Can I locate it under the house?

430.102 says "The disconnecting means shall be located in sight from the controller location".
In the case of most submersible pumps the controller is the pressure switch. If you have the disconnect there I think you have fulfilled the requirement. You could also use a locking switch somewhere else with proper labelling. (using exception 1)

Greg- I agree with you and this might be one of those place that qualifies under 430.102(B) Exception (a) in which case if the pump were submersed it would be impracticable to install a disconnect switch at the motor.

From a practical sense from someone who has lived with a well for the last quarter century, the pressure switch is the first place a person will go to try to fix this thing and that is the best place for the disconnect. Having one down in the well is impractical although I assume someone might want one at the well head. The problem is, unless you have a separate box for the disconnect and the wires feeding the well, it is a distinction without a difference since the line side of the disconnect might still be available to the repairer.

As an OT aside, I finally gave up on screwing with well pressure switches and I put mine on an Amp plug with a Hansen quick disconnect water connection. I keep a "hot spare" so when I am out there in my skivvies at 2 AM I can just swap it out.
I also built a "house" for my well equipment that keeps it out of the weather but I guess "freezing" keeps yours inside. In Florida carpenter ants are the biggest enemy of pump switches. It seems to be a perfect home for them