OLTA was established as a committee of the Federation of Ontario Naturalists in 1997. Known as the Ontario Nature Trust Alliance, it had 14 founding members. In July 2002 the membership now grown to 23 land trusts decided to incorporate as a new independent organization named, The Ontario Land Trust Alliance. This change better reflected the land trust activities of all its members, which now included recreational, agricultural and built heritage as well as natural heritage properties.
These land trusts are non-profit organizations with charitable status established to preserve lands of significance in the communities they serve. Ranging from regional groups in the Rainy River, Thunder Bay and Sault Ste. Marie areas, to the Georgian Bay, Muskoka, London, Oak Ridges Moraine, Kawartha, Rideau and Thousand Islands regions, these organizations are at work throughout the Province. OLTA also includes well-known provincial and national organizations such as Ontario Nature and the Nature Conservancy of Canada.