The latest and last to be added are 700 pictures taken by John Laing photographers for the construction firm's in-house newsletter Team Spirit.
They show workers enjoying company away days at the seaside.
John Laing was founded in Carlisle in 1848 and became one of Britain's biggest construction firms, playing a key role in rebuilding the nation after World War Two.
It arranged company away days, events and trips to the seaside for the families of its workers with photographs taken to record the occasions for the company's newsletter, published from 1946 until 2001.
The photo collection, which has more than 230,000 images, is held by Historic England.
A spokesman said John Laing's management had "enlightened attitudes" towards its staff with a "strong focus on family values".
Historic England chief executive Duncan Wilson added: "Covering everything from seaside adventures to company sports days, these fantastic photographs evoke the joy of holidays and colleagues coming together."