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.
Have a cashflow of $50,000 or more
Build a sandbox prison with 100 prisoners
Loaded a prison from Steam Workshop
Achieve a re-offending rate of 25%
Complete the story
Complete optional objective on Bootstraps
Unlock entire tech tree
Complete all optional objectives on Conviction
Complete all optional objectives on Riot
Build a sandbox prison with 500 prisoners
Build a sandbox prison with 1000 prisoners
Sell your prison and make over $1,000,000 profit
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