Isaac Cathcart (1845–1909) was a well-known businessman and Snohomish County, Washington, pioneer.
Cathcart was born in county Fermanagh, Ireland, in 1845. He was the son of Isaac F. and Charlott (Bushfield) Cathcart.
He migrated to the Pacific Northwest, settling in the area now called Cathcart after him. There, he was a local logger, hotel-keeper and city treasurer. He ran the Snohomish Exchange Hotel. He was one of the organizers of the Snohomish Skykomish and Spokane Railway and Transportation Company in 1891. His large land holdings were purchased by George Hillman who platted and sold the lots, eventually creating the town of Clearview. He was involved in an action in the Washington Supreme Court in 1902.