The Collaborative International Dictionary of English v.0.48:

Hillside \Hill"side`\, n.
   The side or declivity of a hill.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hillside
    n 1: the side or slope of a hill

U.S. Gazetteer Places (2000):

Hillside, NJ -- U.S. Census Designated Place in New Jersey
   Population (2000):    21747
   Housing Units (2000): 7388
   Land area (2000):     2.790366 sq. miles (7.227014 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    2.790366 sq. miles (7.227014 sq. km)
   FIPS code:            32010
   Located within:       New Jersey (NJ), FIPS 34
   Location:             40.695552 N, 74.228561 W
   ZIP Codes (1990):     07205
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Hillside, NJ
    Hillside


U.S. Gazetteer Places (2000):

Hillside, NY -- U.S. Census Designated Place in New York
   Population (2000):    882
   Housing Units (2000): 344
   Land area (2000):     0.840934 sq. miles (2.178008 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.840934 sq. miles (2.178008 sq. km)
   FIPS code:            34786
   Located within:       New York (NY), FIPS 36
   Location:             41.921923 N, 74.033217 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Hillside, NY
    Hillside


U.S. Gazetteer Places (2000):

Hillside, IL -- U.S. village in Illinois
   Population (2000):    8155
   Housing Units (2000): 3107
   Land area (2000):     2.147525 sq. miles (5.562063 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    2.147525 sq. miles (5.562063 sq. km)
   FIPS code:            35086
   Located within:       Illinois (IL), FIPS 17
   Location:             41.874797 N, 87.900372 W
   ZIP Codes (1990):     60162 60163
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Hillside, IL
    Hillside