Merrill is a city in Klamath County, Oregon, United States. The population was 844 at the 2010 census. Merrill is an agricultural area and is ho…Merrill is a city in Klamath County, Oregon, United States. The population was 844 at the 2010 census. Merrill is an agricultural area and is home to an annual Potato Festival. The area was also part of the Klamath Basin water crisis pitting agricultural interests against endangered species water requirements, tribal interests, and environmentalists.