Pioneering studies during 1980s and 90s in the Chesapeake Bay watershed showed that atmospheric deposition was a major contributor of nitrogen (N) loads, providing 1/3 or more among all sources and a principal driver of hypoxia in the Bay. Reducing atmospheric N deposition later became part of efforts to reduce N loads to the Bay in a previously unprecedented merging of goals under the Clean Air and Clean Water Acts. Atmospheric N deposition has shown sharp declines since 1995 as the 1990 Amendments to the Clean Air Act were implemented. Wet and dry deposition measurements at sites in the Chesapeake Bay airshed indicate decreases in oxidized N deposition of 60% to 72% synchronous with declines in oxidized N emissions during 1995-2019. Reduced N, however, shows contrasting patterns; NH₃ emissions have likely changed little during 1995-2019, and wet NH₄⁺ deposition accordingly has shown no trend. However dry NH₄⁺ deposition has declined by 73% during this period. Dry NH₄⁺ deposition is controlled in part by formation of NO₃^- and SO₄^2- aerosols resulting in some asynchrony with NH₃ emissions. A century-long atmospheric deposition N time series was developed for 1950-2050 using measurement-modeling fusion and projections based on clean air regulations. This time series shows a peak in atmospheric N deposition of 15 kg N/ha/yr in 1979, a slight decline by the mid-1990s, sharp 40% decreases during 1995-2019, and further decreases of 21% thereafter through 2050. These deposition estimates were compared with century-long watershed estimates of N loads from manure, fertilizer, and wastewater. Atmospheric N deposition was estimated to be 30% of the total N load to the watershed in 1950, reached a peak of 40% in 1973, declined to 28% by 2015, and is projected to further decrease to 24% by 2050. These data indicate the importance of atmospheric N deposition in the Chesapeake Bay watershed and highlight that implementation of the Clean Air Act has contributed to reducing nutrient loads and improving estuarine trophic status.