Hi and welcome to JustAnswer!. This is Ed.
Well, something's stuck... that's for sure. Your finding that the steering wheel isn't a factor is great info.
All that remains is the ignition lock cylinder or the electrical portion, the actual ignition switch. You will probably have to pull the electrical switch off to be able to tell which one is at fault.
To begin with, there's the standard precautionary advice of disconnecting the battery before working in the proximity of an airbag. Good advice -- disconnect your battery and wait two minutes to allow the capacitors to discharge.
The column tilt lever will need to be removed. It pulls off with considerable effort in a straight-left direction.
Then remove the steering column shrouds halves, the covers that sit just forward of the steering wheel. You'll have three #20 Torx screws to remove and two of 'em are deep. You'll need a long-shafted T-handle or a Torx driver (like a screwdriver) to reach the fasteners. The key will have to be removed for removal of the lower shroud.
Now, on the left-lower side of the column, you will see a bracket that supports the tilt lever and cable. Torx screws are once again used, but you'll need some different sizes... perhaps a 25 or 30. Lower the bracket to gain access to the switch.
Now the switch is within your grasp, but won't give up without a fight. Two smaller Torx screws (could be a 10) sit on the seat-side of the switch and need to be removed. The electrical connector has a red slide-lock that needs to be clicked (not removed) to its opposite position, then the thumb tab will allow its release. Then pry two finger tabs that stretch over the column (like grasping arms) and pry the switch away from the column.
Now removed, see if the key will turn. If it does, it shows that the electrical switch was the problem. If not, we need to get the key to rotate or the lock cylinder can't be removed without breaking the column.
I'm guessing this is where we're headed.
Chances are good that you have an expensive key, one with RKE buttons on it... and probably an RFID chip to disarm the immobilizer. What we're going to have to do next just plain isn't good for these keys, so I recommend that you go to a place where a cheap, all-metal key can be cut because it's probably going to get some abuse. It's best to do it to a $5 key.
New crappy key in hand now? Good... we can proceed. Hammer time.
First, try the new key. Over and over. Wiggle, jiggle, even use increased turning force with some pliers, but be careful to avoid bending or breaking the key. If it turn, skip ahead. If not, we'll need a hammer.
Tap the key directly into the lock cylinder as you would with a nail, while maintaining turning force on the key. Tapping is effective if a small piece of debris has come loose and is sitting in the base of the lock cylinder, preventing it from dropping all the way into the hole. If it can't reach bottom, the key slots won't align with the tumblers and the cylinder can't turn. Tapping it may get you that last little bit of seating necessary to get the cylinder to turn, which is needed for removal.
With the key now turned to the RUN position, look directly up from below at the base of the column, where the lock cylinder slides. A small hole will be present and this is where you need to push a small screwdriver (or #15/ smaller Torx driver) to depress the lock tab that holds the cylinder in the column casting. As you push the tab, pull on the key and it should drop right out.
To get a new lock cylinder, drop by your local Dodge/ Chrysler/ Jeep/ Ram dealer with a VIN in hand, as they'll need to access your build information to obtain the key code your Durango was built with. It will be configured as you wait, or better yet... done over the phone and will be waiting for you when you get there. Expect this part and service to cost less than $100, but not by much.
Installation of the new lock cylinder (or electrical switch, whichever was needed) is pretty much what I've described in reverse. You'll need to rotate the key a bit to spline up with the electrical switch, but other than that, you're almost home.
Let me know if you have any questions or problems and I'll do my best to help. Unfortunately, if you can't get the key to turn (even with the strong but crappy key), you're kind of hosed. Everything depends on getting the key to rotate.