So after graduating Hollerith became an assistant to Trowbridge, first at Columbia University but later he joined the US Census Bureau as a statistician when Trowbridge was appointed Chief Special Agent to the Census Bureau. This appointment was very significant because it was in solving the problems of analysing the large amounts of data generated by the 1880 US census that Hollerith was led to look for ways of manipulating data mechanically.
Kaya pagkatapos ng graduating Hollerith ay naging isang assistant sa Trowbridge, una sa Columbia University ngunit mamaya siya sumali sa US Census Bureau bilang isang estatistiko kapag Trowbridge ay hihirangin Chief Special Agent sa Census Bureau. Appointment na ito ay napaka-makabuluhan na ito sapagkat ito ay sa nilulutas ang problema ng analysing ang malaking halaga ng data na binuo sa pamamagitan ng 1,880 US senso na Hollerith ay humantong sa hitsura para sa mga paraan ng pagmamanipula ng data wala sa loob.