Here is the full list of all 18 Prison Architect achievements. It takes around 50-60 hours to unlock all of the achievements on Windows.
Build a sandbox prison with 100 prisoners
Unlock entire tech tree
Complete all optional objectives on Riot
Achieve a re-offending rate of 25%
Loaded a prison from Steam Workshop
Complete the story
Complete all optional objectives on Conviction
Complete optional objective on Bootstraps
Build a sandbox prison with 500 prisoners
Build a sandbox prison with 1000 prisoners
Sell your prison and make over $1,000,000 profit
Have a cashflow of $50,000 or more
Stopped a riot of 50 or more prisoners
Executed a prisoner on death row
Unlocked all polaroids
Unlocked all game bible pages
Escape from a decent prison in escape mode
Shared a prison via Steam Workshop