King's Highway 4, also known as Highway 4, is a provincially maintained highway in the Canadian province of Ontario. Originally much longer than its present 100.8 km (62.6 mi) length, more than half of Highway 4 was transferred to the responsibility of local governments in 1998. In its present form, it travels between Highway 3 in Talbotville Royal, north-west of St. Thomas, and Highway 8 in Clinton.