There are a total of 82 collectible locations in the game Thief.
Finding all collectibles will unlock the What's Yours is Mine trophy / achievement.
One collectible is obtained automatically during the prologue and cannot be missed. The rest is scattered across all main missions, client jobs and the open world (The City) and you can find them by looking this video.
-TIMELINE:
0:15 - Hand Tailored
8:18 - Silence is Golden
14:27 - Heartbroken