1900 Census microfilms at Internet Archive

Reel 153. Kent County (part: EDs 66-74 and ED 75, sheets 1-10)
Reel 154. Kent (cont'd: ED 75, sheet 11-end) and New Castle (part: EDs 1-21 and ED 22, sheets 1-12) Counties
Reel 155. New Castle County (cont'd: ED 22, sheet 13--end, and EDs 23-39)
Reel 156. New Castle County (cont'd: EDs 40-60, 103, 104, 61, and ED 62, sheet 1)
Reel 157. New Castle (cont'd: ED 62, sheet 2--end) and Sussex Counties