Middlesex is one of the 39 historic counties of England. Located in the south east of England, its area now lies almost entirely in the ceremonial county of Greater London having been abolished in 1965, and much of its area transferred to the County of London in 1889. Smaller parts now lie within the counties of Hertfordshire and Surrey. Middlesex's boundaries largely followed three rivers: the Thames in the south, the Lea to the east and the Colne to the west. A line of hills formed its northern boundary with Hertfordshire. The county was the second smallest of the historic counties of England, after Rutland.