TILT conserves over 7000 acres of land. Roughly half of it is privately owned land subject to conservation easements held by TILT. Landowners have voluntarily placed easements on their property, limiting their development rights in some way, in order to protect natural attributes of the land.

The other half is land that is owned by TILT and falls into several categories. There are four preserves, and also wetlands, forest land and grasslands on Grindstone Island, Wellesley Island and the mainland. These properties were donated to TILT by people who wished to conserve their special characteristics for the benefit of future generations. The land trust also acquired numerous rocks and shoals through quit-claim deed. These tiny islets are important wildlife habitat, as well as being unsuitable for development.