MD 144 begins at the county line as two-lane undivided Frederick Road, where the state highway passes through the Ellicott's Mills Historic District. The state highway parallels the Patapsco River east to River Road, where the highway gains an eastbound climbing lane and leaves the steep river valley. MD 144 passes several loops of old alignment on the ascent, which concludes shortly after passing Old Frederick Road. MD 144 continues east through a densely populated residential area, intersecting North Rolling Road and entering Catonsville, where the highway intersects MD 166 (South Rolling Road), which heads south toward the University of Maryland Baltimore County and Baltimore/Washington International Thurgood Marshall Airport (via I-195). The state highway passes close to the historic home Summit and passes between the Old Catonsville Historic District and Central Catonsville and Summit Park Historic District as it enters downtown Catonsville, which contains Old Catonsville High School. At the eastern end of the central business district, MD 144 passes Wade Avenue, which heads south to Spring Grove Hospital Center, before meeting I-695 (Baltimore Beltway) at a diamond interchange.