Melanie,

Your plant is Viola sororia f. Priceana, the Confederate violet.

It is one of the variants of V. sororia, the sister violet (it goes by several other common names as well).
The normal plant has violet-blue flowers, but there are white-flowered variants; and in a way yours is in-between.

There are also reddish flowered ones, and a reddish equivalent of yours, called 'Alice Witter'.

One of the most commonly grown cultivars is 'Freckles', which as white petals heavily marked with blue freckles.
There are also cultivars with variegated leaves, eg. 'Binstead Speckles'.

They are all tough and hardy plants, increasing well by seed and division (a lawn mower will do the trick!)
So perhaps if you don't want them in your sod, hmmmmm

They are not poisonous as such, and many types of violet have been used for medicinal and food purposes for a long time. But, to genealize, it would be safest to eat the leaves and flowers rather than seeds or roots. And as with most things - in moderation. If you want to use any violet as a foodplant, I strongly suggest you do further research (easier now you know what it is, eh?)

Mike

Here is a link that might be useful: {{gwi:1338457}}

Thank you for the ID :-) Even though I haven't noticed them spreading by seed, I will be sure to keep the plants far from the new sod.