Match report says 30,760 (right at the bottom).
https://www.brightonandhovealbion.com/news/3810653/hinshelwood-heads-the-winner-as-albion-come-from-behind
The post-match display on the big screen said 30,000 and change (I can't remember if it was 30,700 or 30,070). Since the goal came early enough, I'm sure none of them had left to get the train.