 PA 999 was designated in 1928 between Millersville and U.S. Route 30 (US 30)/PA 1 (now PA 462) in Lancaster.The route was extended west to its current terminus at PA 441 in the 1950s.PA 999 begins at an intersection with the southern terminus of PA 441 in the community of Washington Boro, located on the east bank of the Susquehanna River in Manor Township, Lancaster County, heading east-northeast on two-lane undivided Penn Street.