What would happen legally to me if I walk away from my home?
First of all, are you behind in payments? If your behind then you can request a short sale and depending on the lender they will either allow or not allow the short sale. Yes, it would go on your credit report. If you walk away, you still owe whats left on the mortgage and legally you would be abandoning the property which has consequences if something should happen.
this happens with some regularity these days.

least troubling is if you call mortgage company and arrange a deed in lieu of foreclosure. saves everyone time and costs.

after they take ownership, they'll sell the house and depending on the state and your contract, they'll send you a bill for the shortfall on the sale, if any, or a check for the excess of the sale over the mortgage debt [less costs, of course]. not many checks are being sent out.

most folk in this situation can't pay the shortfall so the mortgage company will write it off as a loss [eventually] and will send you a notice that they've reported the amount to the IRS as income to you.

[can't keep up with which years this paper "income" is taxable and which years it isn't.]

meanwhile, you need to find somewhere else to live that you can actually afford.

GL
You would get a foreclosure on your credit report.

You may be liable for the difference. Either through a 1099 or law suit.

Why not try and modify? If you just cannot afford it period, then shortsale it. You have a better chance at not getting a deficiency judgement and negotiating a better settlement for yourself.
Contact as many of the "we buy houses" types you can. Look online for real estate investors. If you are thinking about walking away–get something out of the transaction. Put a ad in the paper-say take over payments for $1000.00. Or an amount that is acceptable to you. Better to try then to just walk away. Someone will take that house from you. If you are in Illinois–drop me a line.
TALK to your lender, keep calling and talking to them and asking them what options are available.
Walking away is generally NOT the best option
ASK for loan modification, lowering interest rate and lowering payments
Talk to Loss Mitigation department
Consider trying to Short Sale property, Deed in Lieu of Foreclosure
why not rent it out? or rent out a room there to help pay for the mortgage.
foreclosure.