Where in the world?
The flag of Sierra Leone has three horizontal stripes of green, white, and blue.

Sierra Leone

Population: 7,976,985

Region: Africa

Subregion: Western Africa

Capital: Freetown

Top Level Domain: .sl

Currencies: Sierra Leonean leone

Border countries

The flag of Guinea has three vertical stripes of red, yellow, and green.

Guinea

Population: 13,132,792

Region: Africa

Capital: Conakry
The flag of Liberia has eleven horizontal stripes of red and white, with a blue square in the upper hoist-side corner containing a white five-pointed star.

Liberia

Population: 5,057,677

Region: Africa

Capital: Monrovia