CREATE TABLE table_1900 ("Township" TEXT, "County" TEXT, "Pop.  ( 2010 ) " FLOAT, "Land  (  sqmi  ) " TEXT, "Water  ( sqmi ) " TEXT, "Latitude" TEXT, "Longitude" TEXT, "GEO ID" FLOAT, "ANSI code" FLOAT)

Name the least ansi code for 609 population 2010
SELECT MIN("ANSI code") FROM table_1900 WHERE "Pop. (2010)" = '609'
SELECT MIN("ANSI code") FROM "table_1900" WHERE "Pop. (2010)" = '609'