Complex sentence: Multnomah County (IPA:) is a county located in the U.S. state of Oregon, the smallest Oregon county in terms of size, but the largest in terms of population due to Portland, which is the county seat and largest city in Oregon.
Split into simpler sentences: Multnomah County (IPA:) is a county located in the U.S. state of Oregon. It the smallest Oregon county in terms of land area, but is the most populous as its county seat, Portland, is the largest city in Oregon.