[DX] Simple Cell Data From Vertex Data

I've created a terrain mesh with the same size triangles. I store cell data for every 2 triangles. I have 60 vertices per row and 60 vertices per column. When creating the vertices I store every 6 vertices in a collection as a cell for collision detection later. The problem with this is that it creates 10 cells per row and not 60.

60 vertices / 6 = 10 cells. I should have 60 cells.

Since each cell shares vertices from another, how can I calculate this? How can I determine which vertices to re-use when creating the next cell?

I know this should be pretty easy but I'm stumped...