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