What county is Gresham OR in

Gresham city is located Multnomah County.

Gresham Location: Country United States, State Oregon, County Multnomah. Nearby cities and villages : Wood Village, Fairview and Troutdale.

Is all of Gresham in Multnomah County?
Is Gresham part of Clackamas County?
What is considered Multnomah County?
What is the county for Portland OR?