Seneca, OR has a population of 180 and is the 24,910th largest city in the United States. The population density is 226 per sq mi which is 472% higher than the Oregon average and 150% higher than the national average. The median age in Seneca is 57 which is approximately 46% higher than the Oregon average of 39. In Seneca, 69% of the population over 15 years of age are married, 99% speak English and 1% speak Spanish. 65% of Seneca residents were born in Oregon, 35% were born out of state, 0% were born outside of the United States and 0% were foreign born.