This is much simpler than Mike indicated.
The sale is not taxable. You simply reduce your cost basis in your property. For example, if you paid $100,000 for the land and the house, and the county paid $2000 for the strip used for the road, then your cost basis is now $98,000. If and when you sell the property, your capital gains will be calculated from your adjusted basis rather than your original basis.
You don't have to know what the original "cost" of that strip of land was to determine a gain on the transaction, you just treat it as though they bought $2000 worth of your land for $2000, so there's no capital gain or loss, you just broke even (which is why it is not taxable). And if they bought $2000 worth of your land (in my example) then the adjusted cost of your remaining land is reduced by the purchase price of the strip. (If you sold your land next year for $150,000, then your profit would be $52,000 instead of $50,000, and that's where the tax comes in, if you owe any. But you deal with it later.)
The only case where you would owe current tax is if the price paid for the strip was more than the total price you originally paid for the house and land.
