Brunswick is a city in southwestern Frederick County, Maryland, United States. The city is located on the north bank of the Potomac River; L…Brunswick is a city in southwestern Frederick County, Maryland, United States. The city is located on the north bank of the Potomac River; Loudoun County, Virginia occupies the opposite shore. The population of Brunswick was 8,211 at the 2022 Census. There are three schools serving Brunswick: Brunswick Elementary School, Brunswick Middle School, and Brunswick High School.