Lincoln County is a county located in the U.S. state of Montana. As of the 2020 census, the population was 19,677. Its county seat is Libby. The county was founded in 1909 and named for President Abraham Lincoln. The county lies on Montana's north border and thus shares the US-Canadian border with the Canadian province of British Columbia. This heavily wooded and mountainous county once was part of Flathead County until residents of Libby and Eureka petitioned the state legislature for separation. Libby won an election over Eureka to host the county seat.