While no official statistics exist, Spades is widely reported as the most played card game in U.S. prisons. Here's why, plus other common games:
Card games provide structure, social bonding, mental escape, and informal economy. Spades especially carries cultural significance in African American communities, tracing to Bid Whist and Bridge traditions.
Popularity varies by facility, region, population, and contraband access. But if you hear cards shuffling in a dayroom, it's probably Spades.