There are a variety of online resources available for Trenton research.
National Register of Historic Places - Wikipedia list (Mercer County)
New Jersey and National Registers of Historic Places - NJHPO (Mercer County)
New Jersey and the Great War (WW1 Centennial)
R.C. Maxwell Company Records (Duke University)
Julian and Gregorian calendar conversion (Wikipedia)
City of Trenton
Division of Vital Statistics (birth, death, marriage certificates)
Trenton Genealogy Resources (Trenton Historical Society)
Birth records from May 1, 1848 to May 31, 1878. Note: more than half of all births during this time period were not recorded. For an indirect reference to these births, it is necessary to search the census records.
Death records from May 1, 1848 to May 31, 1878
Marriage records from May 1, 1848 to May 31, 1878
Birth, marriage and death records starting at 1919
Domestic partnership records starting at 2004
Civil union records starting at 2007
Adoptions – foreign and domestic
Certificate of Birth Resulting in Stillbirth data starting at 1969
The 1890 United States census was destroyed due to water damage caused by a fire in the federal building where it was being held. The only 1890 census left is the special Civil War veterans’ schedule.
Some of these websites require a paid subscription but may offer a free trial
Random Acts of Genealogical Kindness - New Jersey