Statewide Census Records that exist for Delaware are 1790, 1800, 1810, 1820, 1830, 1840, 1850, 1860, 1870, 1880, 1890(fragment, see below), 1900, 1910, 1920, 1930 and 1940.
There are Industry and Agriculture Schedules 1870 and 1880; the Mortality Schedules for the years 1870 and 1880; and the Union Veterans Schedules for 1890.
Delaware federal census records are complete from 1800 onward. They can be found in a number of places and are even properly indexed. However, the records for the 1790 census have been lost.
Nevertheless, some tax assessment records were used to create the Reconstructed 1790 Census of Delaware, a published compilation, which may not be entirely accurate. The slave schedules for 1850 and 1860 and the original death schedules have been published.
The Delaware Public Archives holds census records for 1850-1880, as well as other schedules. Older tax records and other records have also been compiled into censuses of sorts and are on record at the Delaware Public Archives.
Searchable Delaware Census Databases