This is the northernmost light station in Maine. The first light here was a red lantern that hung from a tree on the south bank of the St. Croix river. The station was upgraded in 1910, when a more conventional lighthouse was built. It's named for a Mr. Whitlock who tended the first lantern and owned a mill nearby. Unlike the other light stations, this river light only operated seasonally, closing in winter when the St. Croix becomes a frozen corridor of ice. The light was automated in 1969 and still functions as a navigational aid, but it is privately owned and not open to the public. It can be seen from a dirt road near the Taylor Furniture store on Route 1, just south of Calais.
Whitlocks Mill Light Station was built in 1892.