This dataset includes stable carbon isotope values, lignin, cellulose, and hemicellulose concentrations (expressed as percent of ash-free dry mass) for riparian cottonwood (Populus deltoides) tree rings growing on the Little Missouri River floodplain, Theodore Roosevelt National Park, North Dakota. Drought stress induces stomatal closure and the carbon isotope ratio of annual tree rings tends to be negatively correlated with water availability, especially in dry environments. However, lignin and hemicellulose can obscure annual trends in carbon isotope compositions as these wood components can differ in δ13C relative to pure cellulose. We measured δ13C of whole wood in annual tree rings from seven trees with oldest rings that ranged from 1791 to 1972. These data were used in tandem with lignin, cellulose, and hemicellulose concentrations to explore changes with tree age and the extent to which δ13C correlates with river flow, precipitation, and temperature. There are four files in this dataset: 1) a comma delimited machine-readable file (.csv) that represents the data dictionary for the stable isotope data, 2) a comma delimited machine-readable file (.csv) that represents the data dictionary for the lignin, hemicellulose, and cellulose concentration data, 3) a comma delimited machine-readable file (.csv) containing the stable isotope data, and 4) a comma delimited machine-readable file (.csv) containing the lignin, hemicellulose, and cellulose concentration data.