I split 1/3 of land off and left 2/3 with a house on it. Orig. cost basis of total property was 65667. Sold 1/3 for 5K and 2/3 for 65K. What is cost basis of 1/3 parcel?

I suggest you look up the values assigned to the land and the improvements (house) on the county tax assessors office.  Use that ratio to determine what part of the cost basis was land and what part was the house.  Then take 1/3 of that and that is a reasonable way to determine the cost basis for that part of the land. 

For example, the tax assessor says the land is worth $90,000 and the "improvements" are worth $110,000 for a total value of $200,000 (ignore what the actual value is).  The ratio of land to total value is $90,000 / $200,000 or 45%.  So of the original cost basis of $65,667, the land was 45% or $29,550.  One third of the cost basis of the land would have been $9,850.

Thanks so much! I have a follow up question: using your info I would then reduce the original Cost Basis of the remaining 2/3 (with the house) like so: $65,667 minus $9,850 equals $55,817. This would be my new Cost Basis.

And for the sale of the 1/3 parcel, my Cost Basis would be $9,850 (even though I sold it for $5,000) which shows a loss. Is this correct?

Thanks so much! I have a follow up question: using your info I would then reduce the original Cost Basis of the remaining 2/3 (with the house) like so: $65,667 minus $9,850 equals $55,817. This would be my new Cost Basis.

And for the sale of the 1/3 parcel, my Cost Basis would be $9,850 (even though I sold it for $5,000) which shows a loss. Is this correct?

Thanks so much! I have a follow up question: using your info I would then reduce the original Cost Basis of the remaining 2/3 (with the house) like so: $65,667 minus $9,850 equals $55,817. This would be my new Cost Basis.

And for the sale of the 1/3 parcel, my Cost Basis would be $9,850 (even though I sold it for $5,000) which shows a loss. Is this correct?

Thanks so much! I have a follow up question: using your info I would then reduce the original Cost Basis of the remaining 2/3 (with the house) like so: $65,667 minus $9,850 equals $55,817. This would be my new Cost Basis.

And for the sale of the 1/3 parcel, my Cost Basis would be $9,850 (even though I sold it for $5,000) which shows a loss. Is this correct?