1840  -- the towns of southern Westchester County (now the Bronx) were:

Yonkers (west of the Bronx River and in the northwest section of the future Bronx);
Eastchester (east of the Bronx River and east of Yonkers);
Westchester (located south of the towns of Yonkers and Eastchester); and
Pelham (northeast section of the future Bronx and along Long Island Sound).

1874  --  before this year, the entire area of the Bronx was part of Westchester County.  In 1874 the portion west of the Bronx River (the towns of Morrisania, West Farms and Kingsbridge) was annexed to New York City. 

1888 -- A commission purchases Van Cortlandt Park, Bronx Park, Pelham Bay Park, Crotona Park, Claremont Park, St. Mary's Park, Mosholu Parkway, Pelham Parkway, and Crotona Parkway, thereby founding the park system of The Bronx (today covering 24% of the borough's land surface).  Half of Bronx Park and all of Pelham Parkway and Pelham Bay Park were located outside of the city's boundaries of the time.

1895  --  the portion of the Bronx east of the Bronx River (the town of Westchester and parts of the towns of Eastchester and Pelham) was annexed to New York City.

1898  --  both halves of the Bronx (west and east of the Bronx River) were consolidated into Greater New York City.

1914  -- the Bronx became a separate county on a par with the other boroughs.

Modern Bronx Community Districts:

Far West  Central Far East
Kingsbridge Heights-Bedford                       
Fordham-University Heights
Mott Haven-Melrose
Belmont-East Tremont                      
Morris Park-Bronxdale
Hunts Point-Longwood 
Parkchester-Sound View 
Throgs Neck-Co-op City                                     

(Source: Gonzales 2004:136)