 It cuts across the northeastern corner of Baltimore County and into Harford County, where it runs through Rocks State Park, Palmer State Park, and Susquehanna State Park, passing north of the Bel Air area.The only dam on Deer Creek, the Wilson Mill Dam, is located along Glenville Road in Harford County.A Denil (baffle) fish ladder was built beside the dam in 2000, re-opening approximately 25 miles of spawning habitat to several anadromous fish species.