Below are federal and state censuses by year. Union county was formed in 1857 out of Essex county, New Jersey.
| Year | Type | Description | Series | Film # |
| 1790 | federal | Essex and most of state | not extant | |
| 1800 | federal | Essex and most of state | not extant | |
| 1810 | federal | Essex and most of state | not extant | |
| 1820 | federal | Essex and most of state | not extant | |
| 1830 | federal | Bergen and Essex County | M19 | 79 |
| 1840 | federal | Essex County | M704 | 250, 251 |
| 1850 | federal | Essex County (Free Schedule) | M432 | 449, 450 |
| 1850 | federal | Slave Schedules for Entire State | M432 | 466 |
| 1855 | state | Union County | not extant | |
| 1860 | federal | Union County | M653 | 710 |
| 1865 | state | Union County | 1 reel | |
| 1870 | federal | Union County | M593 | 890, 891 |
| 1875 | state | Union County | not extant | |
| 1880 | federal | Warren (cont.) & Union Counties EDs 1-175, sheet 30 | T9 | 800 |
| 1880 | federal | Union County (cont.) ED175, sheet 31 to end | T9 | 801 |
| 1885 | state | Union County | 1 reel | |
| 1890 | federal | Union County and rest of state | not extant | |
| 1890 | federal | Union Veterans & Widows of Civil War (Hudson, Hunterdon, Mercer, Middlesex, Somerset, and Union counties) | M123 | 42 |
| 1895 | state | Union County | 2 reels | |
| 1900 | federal | Sussex (cont.) & Union Counties | T623 | 995 |
| 1900 | federal | Union County (cont.) | T623 | 996 |
| 1900 | federal | Union (end) & Warren Counties | T623 | 997 |
| 1905 | state | Union County | 2 reels | |
| 1910 | federal | Sussex & Union Counties EDs 50-70 | T624 | 909 |
| 1910 | federal | Union County EDs 71-100, 155 | T624 | 910 |
| 1910 | federal | Union EDs 101-120 & Warren Counties | T624 | 911 |
| 1915 | state | Union County | 4 reels | |
| 1920 | federal | Union County EDs 57-60, 109, 110, 61-74, 92-95, 104-107 | T625 | 1069 |
| 1920 | federal | Union County EDs 75-91, 96-103 | T625 | 1070 |
| 1920 | federal | Union County EDs 108, 111-117, 136-144, 152, 153, 118-135 | T625 | 1071 |
| 1920 | federal | Union EDs 145-151, 154-167 & Warren Counties | T625 | 1072 |
|
federal |
Union County |
T626 |
1385-1390 |
|
| 1940 | federal | Union County EDs 20-1 to 20-36 | T627 | 2385 |
| 1940 | federal | Union County EDs 20-37 to 20-63 | T627 | 2386 |
| 1940 | federal | Union County EDs 20-64 to 20-99 | T627 | 2387 |
| 1940 | federal | Union County EDs 20-100 to 20-130 | T627 | 2388 |
| 1940 | federal | Union County EDs 20-131 to 20-166 | T627 | 2389 |
| 1940 | federal | Union County (Elizabeth) EDs 20-167 to 20-211 | T627 | 2390 |
| 1940 | federal | Union County (Elizabeth) EDs 23-1 to 23-35 | T627 | 2397 |
| 1940 | federal | Union County (Elizabeth) EDs 23-36 to 23-61 | T627 | 2398 |
| 1940 | federal | Union County (Elizabeth) EDs 23-62 to 23-87 | T627 | 2399 |
| 1940 | federal | Union County (Elizabeth) EDs 23-88 to 23-119 | T627 | 2400 |
Census indexes and images are available for free at FamilySearch. Links are available above. Browse by location to search a specific collection.
April 2, 2012: The 1940 census images become available online. Learn more about the records.
The 1940 census images are hosted on multiple sites:
Print out a legal-sized blank 1940 census page. (I do this so I can read what each column is for.)
Find out when the Census Day was held for each decade.
