I hope this helps. If you have an LDS Family HistoryLibrarynear you, order film 1450738. It has many Larocques. It is the records of Notre Dame Church ofOdensburg Birth, Marriage and Burial. There are many Larocques.
I also found on the internet, Anne Cady's Site, the 1870 Census of Oswegatchie (Ogdensburg) with a family (LeRock) that could be who you are looking for. There is a Thomas LeRock and his wife Adelia born around 1846 but no children listed, living next to Gilbert and Laura LeRock, born in the 1830's, and a 4 year old George. Probably their son. There is also a John and Matilda LeRock born in the 1830's, with three of their children. I know that this is before the year you are looking for but I thought it might give you some leads.
I too am related to the Larocque's on both sides of my paternal grandparents. I found out through a marriage record that my maiden name should be Larocque and not Belanger. I am having an awful time trying to find a record of birth for my greatgrandfather who changed his last name to Belanger.
This branch of the Larocques came from the Oka, Deux Montagnes area of Canada. Ste Madeleine de Rigaud Church is another place to look. They came to Ogdensburg in the late 1850's. My father's family lived there from that point. And some of their descendants are probably still there.
If you like, you can email me at my new "address". firstname.lastname@example.org