Northumberland County
Below are a number of links to familysearch.org which will give you direct access to Federal Census schedules. It does require you to create a free account.
Before you get started, you may want to read "Clues in Census Records" from the National Archives, especially if you're new to using these records. Also, even if you think you know everything to know about the 1890 being destroyed by fire, you should still find "The Fate of the 1890 Population Census" a very powerful story.Clues in Census Records, 1790-1840
Clues in Census Records, 1850-1930
The Fate of the 1890 Population Census, Part 1
The Fate of the 1890 Population Census, Part 2 United States Census, 1790
United States Census, 1800
United States Census, 1810
United States Census, 1820
United States Census, 1830
United States Census, 1840
United States Census, 1850
United States Census, 1860
United States Census, 1870
United States Census, 1880
United States Census of Union Veterans and Widows of the Civil War, 1890
United States Census, 1900
United States Census, 1910
United States Census, 1920
United States Census, 1930
United States Census, 1940
United States Census, 1950
Before you get started, you may want to read "Clues in Census Records" from the National Archives, especially if you're new to using these records. Also, even if you think you know everything to know about the 1890 being destroyed by fire, you should still find "The Fate of the 1890 Population Census" a very powerful story.
Please report any broken links.