A cornerstone is the first stone laid in a building. Other stones are set in relation to this stone. It sets the direction of the entire structure. Today cornerstones are mostly ceremonial, and sometimes include time capsules or engravings. Freemasonry has an official ceremony in which oil, wine and grain is used.
Masonic Cornerstones are laid in the Northeast of the building. This is an allusion to the North being a symbol for Darkness and the East the rising sun. It stands for being people being brought from the darkness to the light, from ignorance to enlightment.
Cornerstones have been laid in official buildings in the USA since its very beginning. George Washington, while being the president of the USA presided over the masonic cornerstone ceremony for the US Capitol Building on September 18, 1793.
More Info:
https://www.freemason.com/behind-masonic-symbols-cornerstone/
https://www.thestoryoftexas.com/discover/artifacts/bullock-museum-masonic-cornerstone