I am preparing to build a garage. The power lines to my house currently travel underground where I plan to build. My new footers and frost walls will be in the ground deeper than the cables a currently buried. I am going to have to replace the cables either way but the length of the cable will about double if I have to go all the way around the garage. Can I still put the cables under the garage and if so how far under the footers do the cables have to be? I live in Essex County, New York.

When you say, "cables", do you mean conductors in conduit or direct burial cable?
Do you own this cable or is it owned by the utility?

I am talking about direct burial cable, that I own. I did not plan to put it in conduit, but I can if I need to. It may just be cheaper to move the cable outside the area of the garage.

The way the electrical code is worded, you could run the cable under your new garage as long as minimum burial depths are observed. Is this the best choice is difficult to judge from my chair.
Table 300.5 in code lists the required burial depths of cable relative to the location. If going under the footings puts you at least 24" below grade you will meet the code. You might consider installing a 4" PVC conduit "sleeve" for the cable or place it next to the cable for future should the existing cable ever require replacement.
You can always contact the local electrical inspector for advice... they can be a valuable resource.
Good Luck,