摩尔诺玛县（Multnomah County, Oregon）是位于美国俄勒冈州北部的一个县。成立于1854年12月22日，县治波特兰。面积1,206平方公里 (全州最小)。根据美国2000年人口普查数字，共有人口665,810人 (全州最多)。

Multnomah County /məltˈnoʊmə/ is one of 36 counties in the U.S. state of Oregon. As of the 2010 census, the county's population was 735,334, making it the most populous county in Oregon. Its county seat, Portland, is the state's largest city.

Multnomah County is part of the Portland-Vancouver-Hillsboro, OR-WA Metropolitan Statistical Area, and though smallest in area, it is the state's most populous county.