Last year i purchased a partial interest in 3 lots of land in the state of oregon from my brother in law and?

who was co-owner with my husband. the paperwork i drew up to prove it was an "owner's sale and agreement and earnest money receipt", purchased at a local stationary store, where he acknowledged receipt of $5,000.00 paid by me, the balance of $30,000.00 due him upon the sale of the property. it is completed properly, however it was done in haste leaving no time to have it notarized. it is signed and dated by both of us outlining the details, and i gave him a cashier's check, drawn on a local bank. is this agreement legal and binding if should he decide to change his mind?

Yes, because of substantial performance (though partial performance would do). The legal problem arises from the fact that it won't be an open and shut case if he denies any of the above. You would have to prove your performance. At issue is the fact that the document signed is not properly executed. And, if you live in a jurisdiction like Florida - it specifically doesn't satisfy the "Statute of Frauds" which means you could end up losing your interest because the contract is "void ab intio" - invalid from the very moment it was signed - i.e., no contract exists. So, to quickly remedy this issue, notorize a paper that says what you are all agreeing to is the sale contract "attached hereto" - you could say something like, we forgot to notarize and we are notarizing today with the intent to make valid the contract we didn't notarize then as if we had done so then (but you don't have to). Do it now while everyone is all chummy chummy as you won't get to do it when the fit hits the shan. Ok?

Yes, but getting it notarized even now would be even more insurance.

Not every contract needs to be notorized to make it legal. When you purchase a car, do you have the contract say that you will make your payments on time notorized? You both signed it in good faith and it should be binding. If you have any doubt contact a real estate lawyer and get their opinon. Do not go to a genarl attorney.