He is Officer Khalid Ibrahim, who immigrated with his family in 2006.
The swearing-in ceremony Thursday came less than a year after another local Somali-American, Mohamed Mohamud, was sentenced to 30 years for plotting to bomb a crowded holiday event in downtown Portland.
The arrest of the teenager in 2010 sent shock waves through the area's Somali community and strained relations with law enforcement agencies.
The bomb plot was an FBI sting: Agents posing as al-Qaida members supplied a fake car bomb. Jurors rejected Mohamud's entrapment defense.
About 8,000 Somalis came to Portland after a civil war drove them into refugee camps.
Ibrahim was born in Mogadishu. He's a Portland State University graduate and interned at the Police Bureau.