August Aleksander Järnefelt (April 2, 1833 – April 15, 1896), was a Finnish general, topographist, governor and senator.
Aleksander Järnefelt was born in Tohmajärvi, the son of crown overseer Gustav Adolf Järnefelt and Aurora Fredrika Molander. Aleksander married Elisabeth Clodt von Jürgensburg at December 22 in 1857 in Saint Petersburg. Their children were Kasper, Arvid, Erik, Ellida, Ellen, Armas, Aino, Hilja and Sigrid. Armas, Arvid and Eero were famous Finnish cultural figures. Aino Järnefelt was married to composer Jean Sibelius.
Aleksander's work was first topography. At his command, in 1870s, many maps from the Uusimaa, Viipuri, Turku and Pori provinces were made.
During the Turkish war (1877–1879), Järnefelt mapped many areas within Russia conquered from Turkey.
Aleksander was governor of Mikkeli in the 1880s and later worked governor as of Kuopio. Aleksander worked as governor of Vaasa in 1888 where he worked for the rest of his life. From 1894 Aleksander also worked with the military law chief in the Senate. Aleksander died at Helsinki on April 15 in 1896, of paralysis.