Landscape structure in the Eastern US experienced great changes in the last century with the expansion of forest cover into abandoned agricultural land and clearance of forest cover for urban development. Quantifying the changes in forest cover is a prerequisite to understanding the potential effects of those changes on ecological processes. In this paper, the spatial and temporal patterns of forest cover from 1914 to 2004 in the Gwynns Falls watershed in Baltimore, Maryland were quantified from historical forest maps and aerial photographs. Changes in forest cover in the watershed went through a similar pattern as that in the Eastern US. A database including six time slices of forest patches --1914, 1938, 1957, 1971, 1999, and 2004 -- was created. The data were analyzed at two scales: the entire watershed and by 3-km distance bands from the urban core extending out to the upper, more suburban end of the watershed. Our results reveal that forest cover within the watershed is dynamic, both temporally and spatially, from 1914 to 2004. The number, size, shape, and spatial distribution of forest patches within the watershed greatly changed over the 100 years. Forest cover became increasingly fragmented even though the total area of forest cover remained largely unchanged. In addition, results from the distance band analysis show an outward shift in the location of high rates of forest cover change. Forest cover tends to be more stable in and near urban centers that have been largely developed, whereas forest cover is more dynamic in areas where urbanization is still in process. The spatial and temporal dynamics of forest cover underscore the need to integrate multi-temporal data layers to investigate the spatial pattern of forest cover and the temporal variations of that spatial pattern.