If I counter a spell with Defy, do they still get +1 at Abandoned Hall?

No, you do not receive the +1 Might from Abandoned Hall if the spell you played is countered.

According to Rule 425.1.b, a spell that is countered is not considered to have been "played." Because the ability on Abandoned Hall requires a spell to have successfully completed its resolution process to be counted as "played," a countered spell fails to meet the trigger condition.

The sequence of events:

1. Initial State: You play a spell. This spell enters the chain as a "Pending Chain Item."
2. Reaction: Your opponent plays Defy targeting your spell.
3. Chain Resolution: The Defy resolves first (LIFO - Last-In, First-Out). It counters your original spell, which is then cleared from the chain and removed from the game process.
4. Trigger Failure: Because your original spell was countered, it never finished the resolution process. Consequently, it is not considered "played" by the game rules, and the triggered ability on Abandoned Hall never enters the chain.

This interaction is consistent across multiple RiftJudge FAQs (including #10646, #10825, and #10782), which confirm that countering a spell negates the ability to trigger "when you play a spell" effects.