Question

What is the counterexample for the city of Portland is in Oregon

Answer 1

A counterexample is a special kind of example that disproves a statement or proposition. 

The counter example for : the city of Portland is in Oregon would be : the city of Portland is in Maine.

The city named Portland can be found in both states.

Answer 2

One possible counterexample would be:

The city of Portland is in Connecticut.

Explanation:

A counterexample is something that proves a statement wrong.  Since the city of Portland is in multiple states (Oregon, Maine, Connecticut, Arkansas, etc.), any of the other states having a Portland would serve as a counterexample.