YOu will file a final 1065 for the partnership LLC with a close date for that business of Jun 30, 2018. Make sure all issued 1065 K-1's are marked as final too. Assuming the same parners will own the S-Corp, all assets need to be removed from the partnership for personal use, and distributed to the owners as appropriate. Same for any inventory if inventory is involved here. Remember, in order to completely and correctly report the partnership as closed, that partnership must "get rid of" all assets, all inventory, and all vehicles, and any remaining cash left in the partnership. The IRS does not consider your partnership closed until absolutely everything is disposed of in one form or another.
Then for the 1120-S which has a completely separate EIN from the partnership, all assets, inventory, and cash are transferred into it as capital contributions by the members the LLC assets, inventory and cash were distributed to. (If you don't do this, then the members will pay taxes on any gains that were distributed to them from the LLC).
Now THIS IS IMPORTANT! If you do this wrong, all the depreciation on business assets will be wrong. For the S-Corp, the start date of the business will be the same start date the partnership started and was opened. IT MUST be the same. Otherwise, you're going to have major issues with prior years depreciation on any and all depreciable assets.
Then the incorporation date will be one day AFTER the partnership LLC closed. See attached picture for the screen I'm referring to in the TurboTax Business program, for the 1120-S.
