The background layer

[gwpriester]

There is a grid that you don't even need to create. Window > Show Grid.

Logically you would think that the Background is the correct layer to use for a grid, but this is not the case.

As Mike points out, you want to use the Guide layer.

You can drag guides from the screen rulers (Ctrl L to show rulers if they are not displayed).

You can also add any lines or shapes to the Guides layer and these will act as snap to guides. (See attached XAR file)