Bremen is a village in Fairfield County, Ohio, United States. The population was 1,479 at the 2020 census. Bremen was platted in 183…Bremen is a village in Fairfield County, Ohio, United States. The population was 1,479 at the 2020 census. Bremen was platted in 1834. The village was named after Bremen, in Germany. The Bremen Oil Field was discovered in 1907, setting off an oil boom, which lasted until the early 1920s. Oil Derrick Days are celebrated every September, as a way for the town to remember its oil industry heritage.