My mom's trust states that when she can no longer take care of herself, I will have POA. Should we find an attorney in the county she lives in?

I think you may be confusing the POA (Power of Attorney) with a trust document. I think possibly you mean that the trust names you as the successor Trustee of your mom's trust if she is unable to serve as her own Trustee, which is quite common. In any event, it is not necessary that your new attorney be from the same county as your mom, so long as they are licensed to practice law in the same state. As for paperwork, there may or may not be a requirement to file the change of Trustees; if the trust owns real estate, then it would be advisable to record the change in Trustee, so that when you sell the house there will be a document showing you have authority to sign the deed, etc.

Yes- if not an attorney in the same county than at least one the same state. If you are named as the Successor Trustee in your Mom's trust or as the Agent in her Power of Attorney, it's best to consult with an attorney to see what your powers will be and what your duties and expectations will be. If your mom has both a trust and a power of attorney, are you named on both? If not, you'll want to talk with the attorney on how to coordinate with the other person that's named.