St. Marys Cement was founded in St. Mary's, Ontario in 1912. They are now a subsidiary of Votorantim Cimentos, a global company based in Brazil. Votorantim Cimentos has locations in the US, Canada, Turkey, Spain, Tunisia, India, and Morocco, as well as several countries in South America. All the locations I checked in the US are either located on/near the Canadian border, or on waterways with easy access to Canada.
http://www.stmaryscement.com/
http://www.votorantimcimentos.com