Thomas Welch or Walsh (November 5, 1742 – July 2, 1816) was a surveyor and judge in Upper Canada. He was born in the Province of Maryland in 1742, the son of Irish immigrants with roots in Wales. He studied in Philadelphia and served with the British Army during the Seven Years' War. He was appointed surveyor in Berks County, Pennsylvania; in 1769, he moved to Maryland. In 1778, he joined the Maryland Loyalists Battalion. He was taken prisoner by the Spanish at Pensacola, Florida and later released in New York City. He led a group of loyalists to New Brunswick; after five years, he returned to Maryland.