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 was appointed surveyor in Berks County, Pennsylvania; in 1769, he moved to Maryland.
Unable to recover his property in the United States, he left for Upper Canada where land was available and settled in Lincoln County, where he was appointed deputy surveyor.
In the same year, his son, Francis Leigh Walsh, succeeded him as land registrar for Norfolk.