Box Elder County is a county at the northwestern corner of Utah, United States. At the 2020 census, the population was 57,666, up from the 2010 figure of 49,975. Its county seat and largest city is Brigham City. The county was named for the box elder trees that abound in the county. Box Elder County is part of the Ogden-Clearfield, UT Metropolitan Statistical Area, which is also included in the Salt Lake City-Provo-Orem, UT Combined Statistical Area. Box Elder County.