Will Legion effect still work if a card I played gets countered?

Yes, your Legion effect will still work if the card you played is countered.

According to RiftJudge FAQ #9463 and #9461, the Legion condition is satisfied the moment a card is Finalized on the chain.

The Sequence

  1. Playing the Card: You play a card. It is placed on the chain as a "Pending Chain Item."
  2. Finalization: You choose targets and pay all costs. The card becomes a "Finalized Chain Item." At this exact moment, the Legion condition is met for the turn.
  3. Reaction: Your opponent plays a card like Defy to counter your card.
  4. Resolution: The counter resolves, and your card is cleared from the chain (per Rule 425.1.a).

Even though your card was countered and did not resolve, the requirement for Legion was already satisfied during the Finalization step. Therefore, any Legion abilities on cards you play afterward that turn will be active.