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Circa 1984, wetlands and deepwater habitats mapped by the National Wetlands Inventory (NWI) covered 899,277 ha, or 9.8% of eastern South Dakota. Of these 899,277 ha, palustrine system wetlands covered 720,704 ha or 80.1% of the total area, lacustrine system wetlands and deepwater habitats covered 150,538 ha or 16.8% of the total area, and riverine system wetlands covered 28,034 ha or 3.1% of the total area. Lacustrine and palustrine wetlands occupied 947,652 wetland basins of which 520,379 were temporary basins covering 157,853 ha, 334,699 were seasonal basins covering 224,004 ha, 76,260 were semipermanent basins covering 292,555 ha, and 1,491 were permanent potholes and lake covering 187,050 ha. Temporary and seasonal basins were most abundant in the James River Lowland and Minnesota-Red River Valley physiographic regions. Seasonal basins were also abundant on the northeastern Missouri Coteau and Altamount moraine of the Prairie Coteau. A total of 24,485 basins with naturally semipermanent water regimes occurred in eastern South Dakota and were most common on the Prairie Coteau. Basins classified with semipermanent water regimes due to the presence of dugouts were scattered throughout eastern South Dakota. The median size of all wetland basins was only 0.16 ha. Of all eastern South Dakota basins, 58.9% were ≤0.2 ha and 74.4% were ≤0.4 ha in size. Only 5.9% of all basins were >2.0 ha and 2.6% were >4. 0 ha in size. Permanent and semipermanent basins were the largest, and temporary basins were the smallest. Plot sampling techniques are commonly used to monitor wetland status. Square, circular, and rectangular plots and plots from 0.64 to 25.60 km2 in size all provided unbiased estimates of the area of wetland basins; however, bias in estimates of the number of basins from these plot shapes and sizes ranged from 0.2% to 77.8%. Bias was correlated with plot perimeter area ratio. Pond counts along U.S. Fish and Wildlife Service transects may be an effective method of indexing ponded wetland basin availability to breeding waterfowl, but transects provide highly biased (approximately 150%) estimates of the number of basins. Stratification using a priori NWI data may be the most efficient method for partitioning the sampling universe. Wetland managers are commonly encouraged to preserve wetland complexes for waterfowl and other wildlife, but complexes have not been adequately described or defined. The definition that I propose is that a wetland complex consists of a set of wetlands or basins temporally or spatially inter-related by biotic, abiotic, or anthropogenic mechanisms. When the phrase is used in publications, authors should explicitly define the spatial extent and characteristics of wetlands or basins within and around the wetland complex they studied to perm it comparisons with other research.