Lake Oswego is a city in the U.S. state of Oregon, primarily in Clackamas County, with small portions extending into neighboring Multnomah and Washington counties. Population in 2020 was 40,731, an 11.2% increase since 2010, making it the 11th most populous city in Oregon. Located about 7 miles south of Portland and surrounding the 405-acre Oswego Lake, the town was founded in 1847 and incorporated as Oswego in 1910.