For the purposes of Walled Village, is a card that was played and immediately trashed considered "in play"?
For example, if I play Mining Village, trashing it for the +2 coin, then play Walled Village, does the Mining village count towards the "no more than one other Action card in play"?
It is not considered in play if it has moved from your play zone to the trash.
The 'no more than one action card in play' trigger will not count mining villages that were played and then immediately trashed.
Sources: forum post by Donald X. (games creator)
http://boardgamegeek.com/thread/682203/description-sheet
Walled Village: When you play this, you draw a card and can play two more Actions this turn. At the start of your Clean-up phase, before discarding anything and before drawing for next turn, if you have a Walled Village in play and no more than two Action cards in play (counting the Walled Village), you may put the Walled Village on top of your deck. If the only cards you have in play are two Walled Villages, you may put either or both of them on top of your deck. Walled Village has to be in play to be put on top of your deck. Walled Village only checks how many Action cards are in play when its ability resolves; Action cards you played earlier this turn but which are no longer in play (such as Feast from Dominion) are not counted, while Action cards still in play from previous turns (duration cards from Dominion: Seaside) are counted, as are Action cards that are in play now but may leave play after resolving Walled Village (such as Treasury from Dominion: Seaside).
The example 'Feast' in the quote is an action with a self trashing ability similar to mining village.
