Dear Mr. Comtois,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located a series titled Compiled Service Records of Soldiers Who Served in the American Army During the Revolutionary War, 1894-1912 in the War Department Collection of Revolutionary War Records (Record Group 93) but were unable to locate a military service record for a Jacob Greff. We also located the Population Schedules for the 1790 Census;1800 Census; 1810 Census; 1820 Census; 1830 Census and 1840 Census in the Records of the Census Bureau (Record Group 29). Digital images of 1790, 1800, 1810, 1820, 1830 and 1840 census records are not available yet in the Catalog but are digitized and available on Ancestry. From 1790 to 1840, only the head of household is listed by name; other household members are merely counted in selected age groups.
On Ancestry, we located all Birth, Marriage & Death results for Jacob Greff; all Census Results; and all Military results using the information provided. There may be a fee for using Ancestry. Instead, you may view these records online at one NARA's facilities for free via a NARA PC. For the nearest NARA location, please consult our web page at https://www.archives.gov/locations/. Also, some of the images from Ancestry are available for free on Family Search at https://www.familysearch.org/en/.
We suggest that you review NARA’s website for tips on how to begin your genealogical research; Immigration Records; and Census Resources for how to access census records that may are digitized in the National Archives Catalog or available on our partners’ websites as well as how to view them for free at a NARA facility. NARA has census schedules on microfilm dating from 1790 to 1930 but data from recent censuses are not available after 1940 due to the 72-year restriction on access to the Census. Most researchers find it helpful to begin with the 1940 Census and work backwards to locate people in earlier generations.
We hope this is helpful. Best of luck with your family research!