Kosianka-Trojanówka [kɔˈɕanka trɔjaˈnufka] is a village in the administrative district of Gmina Grodzisk, within Siemiatycze County, Podlaskie Voivodeship, in north-eastern Poland. It lies approximately 3 kilometres (2 mi) west of Grodzisk, 22 km (14 mi) north-west of Siemiatycze, and 67 km (42 mi) south-west of the regional capital Białystok.