Here is the full list of all 23 Orrstead achievements.
Build 1000 paths.
Reach 1000 population.
Purchase the "Empowered Orr" upgrade.
Purchase the "Hearth & Home" upgrade.
Reach 500 population.
Build a watchtower.
Build a monument of the forest.
Reach 200 population.
Build a library.
Purchase the "Legacy" upgrade.
Build a village house.
Reach 100 population.
Build a powered sawmill.
Build a town hall.
Reach 50 population.
Reach 25 population.
Build a sawmill.
Reach 10 population.
Build a house.
Build Orr.
Reach 2000 population.
Reach 5000 population.
Reach 10000 population.