The Dennis Society had its origins in the Dennis Bus Owners Association, which was originally formed in 1994. Reflecting the founder member's buses, for a short while it was the Aldershot & District Owners Association. Within a year it had re-organised into two parts, one for Aldershot & District bus owners and another for a supporter's group, known as the Aldershot & District Bus Interest Group.

Although a large number of Dennis buses had been delivered to bus companies nation-wide, the initial heyday was the 1930s. The 1948 Transport nationalisation programme seriously curtailed market penetration until much more recent times. Sadly, most pre-war buses were scrapped before the preservation movement gained momentum. Aldershot & District were unaffected by nationalisation and the fleet naturally comprised a large number of Dennis buses from the local factory at Guildford, both before and after World War 2. The buses were well maintained and a long service life was expected. It is hardly surprising then that several of the Dennis buses that have survived into preservation have come from the Aldershot & District fleet.

Recognising that the problem of locating spares and retaining knowledge was not confined only to Aldershot & District vehicles, in 1998 the name was revised to Aldershot & District and Dennis Bus Owners Association. Membership at that time being opened up to any Dennis bus owner. As a result of this the membership grew to include buses from another large Dennis customer, East Kent. The word also spread among owners of some of the few pre war buses that had survived.

As time went by, the supporter's group, The Aldershot & District Dennis Bus Interest Group attracted members from the local Aldershot & District area, including ex A&D employees. Although many members continued actively supporting restored buses, the nature of the club and its newsletter changed slightly as it took on more historical interest and expanded the featured buses to include all makes operated by Aldershot and District and its successor, Alder Valley.

In 2006 the members of the Dennis Bus Owners Association decided to alter the focus and the A&D part of the title was dropped, reflecting the fact that membership comprised a significant proportion of vehicles from elsewhere. To make administration easier and widen the scope for attracting members, the Association also decided at that time to become almost entirely Internet based. This has enabled the cost of belonging to the Association to be reduced, resulting from savings in postage and printing. At the same time, the new web site provides access to more articles and pictures that are much better quality than the previous small printed newsletter could achieve.

Membership has not been restricted just to Dennis bus owners and, over the years, several owners of other Dennis vehicles (some of which have similar mechanical features) joined the Association. A further change took place in 2011 when, at the AGM, it was decided to formally recognise this expanded membership by changing the name to the Dennis Society, altering the structure of the group, and expanding the web site. Plans are afoot to better cater for non-internet members.