Free museums and cheap museums in Portland, Oregon:
OMSI: Admission is $2 on the first Sunday of the month; kids 2 and under are always free.
World Forestry Center: Admission is $2 on the first Wednesday of the month; children 2 and under are always free.
3D Center of Art and Photography: Admission is free on the first Thursday of the month; kids age 14 and under are always free.
Portland Children’s Museum: Free admission on the first Friday of the month from 6-8 p.m.; children under age 1 free daily.
Oregon Zoo: $2 admission on the second Tuesday of the month; 2 and under free daily. Save $1.50 off the price of admission by presenting your MAX ticket.
Washington County Museum: Free admission every Monday. Kids 5 and under always free.
Oregon History Society and Museum: Up to two kids (under age 18) enter free with each paid adult admission on the third Saturday of the month. Kids 5 and under are always free. Annual free day: April 17, 2010.
Portland Art Museum: Free admission on the fourth Friday of every month. Free general admission quarterly in conjunction with Museum Family Day. Kids 17 and younger are always free with paying adults.
Portland Japanese Garden: Free admission on November 11, 2010. Kids 5 and under are always free.
Lan Su Chinese Garden: Kids 5 and under enter free, daily.
Information obtained from: http://www.cascadiakids.com/portland-freebies-save-money-on-your-portland-trip/