I would say disappointed in a person: I am disappointed in my oldest daughter. And disappointed with something: He was disappointed with the result. We are disappointed with our new house.
In/By/ With/ On/ and From are all possible choices with the use of [disappointed]. The context and the structure of the sentences decide which one sounds more correct to the specific context.
I am disappointed by/ In /With the election result. – all works
The convention sponsors were disappointed from the lack of details and am