Department stores appear to be losing ground to newer sorts of retailers. These newer retailers include those referred to as warehouse stores, those called discounters and those focused on a smaller range of particular products, apparel, shoes and accessories only, for example. Whatever the cause, department stores as a group have been in decline for some time now which can be seen clearly in the figures below. While the retail sector as a whole did well during the decade from 1997 to 2007, some segments have been under pressure due to the changes in the way we get things.

Geographic reference: United States
Year: 1997 and 2007
Market size: Number of Establishments: 10,366 and 8,553 respectively.
Market size: Sales: $220.12 and $210.14 billion respectively.
Market size: Employment: 1,795,577 and 1,229,489 respectively.
Source: “Sector 44: EC0744I2: Retail Trade: Industry Series: Preliminary Comparative Statistics for the United States (2002 NAICS Basis): 2007 and 2002,” 2007 Economic Census, available online here. The data from 1997 are from the 1997 Economic Census, after conversion of the data to a NAICS 2002 basis.
Original source: U.S. Department of Commerce, Bureau of the Census.