Marlette is a city in Sanilac County in the U.S. state of Michigan. The population was 1,855 at the time of the 2020 census. The city is surr…Marlette is a city in Sanilac County in the U.S. state of Michigan. The population was 1,855 at the time of the 2020 census. The city is surrounded by Marlette Township, but is administratively autonomous.