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.
Complete optional objective on Bootstraps
Unlock entire tech tree
Complete all optional objectives on Riot
Complete all optional objectives on Conviction
Build a sandbox prison with 100 prisoners
Loaded a prison from Steam Workshop
Achieve a re-offending rate of 25%
Complete the story
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