Dennis O'Brien was born in Lyndoch, Ontario, married Hannah Butler, daughter of Peter Butler (one of the first residents of Coniston), and had five children: Anne, Inez, Margaret, Norma, and Mary.

In some ways, Dennis O'Brien could be viewed as the father of Coniston. During the construction of the railroad, the O'Briens established a general store to provide necessities to the railway crews.  Since the village was not an organized community and did not even have a name, postal services were not available to the residents.  Instead, they had to travel all the way to Sudbury to pick up their mail.

Dennis O'Brien decided to approach the government to request postal service to the area but was quickly informed that the community needed a name before such a request could even be considered.  O'Brien made organized a search for a suitable community name.  After many submissions, a railway superintendent suggested 'Coniston' after the Coniston Lake District in Northern England, the setting in a book he had been reading.  With the acceptance of the name, the community was now able to arrange for postal delivery and Dennis O'Brien was appointed at the town's first Postmaster. 

The O'Briens managed the post office and general store at its original location until in 1912, the Mond Nickel Company arrived and moved the post office to Second Avenue (where it stands today).  The Coniston Post Office has stayed in the O'Brien family for many generations.

Dennis O'Brien served as a Separate School Trustee as far back as 1918 and for many years, he served as part of the Neelon-Garson Township Council.  The O'Brien name is well respected within the Coniston community thanks to the efforts of this great man.

Material compiled from The Coniston Story II.