In 2003, Hillier co-founded and served as the first president of the Lanark Landowners' Association. He then assisted in creation of local landowner groups in other parts of Ontario, modelled on the Lanark Landowners. In 2006, he became the first president of the 15,000-member Ontario Landowners Association (OLA), an umbrella group for these groups. The OLA was formed "...to preserve and protect the rights of property owners and to enshrine property rights within the Constitution of Canada and the laws of the Province of Ontario."