The Collaborative International Dictionary of English v.0.48:

Letts \Letts\ (l[e^]ts), n. pl.; sing. Lett (l[e^]t).
   (Ethnol.)
   An Indo-European people, allied to the Lithuanians and Old
   Prussians, and inhabiting a part of the Baltic provinces of
   Russia.
   [1913 Webster]

U.S. Gazetteer Places (2000):

Letts, IA -- U.S. city in Iowa
   Population (2000):    392
   Housing Units (2000): 151
   Land area (2000):     0.554986 sq. miles (1.437406 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.554986 sq. miles (1.437406 sq. km)
   FIPS code:            44715
   Located within:       Iowa (IA), FIPS 19
   Location:             41.329049 N, 91.236356 W
   ZIP Codes (1990):     52754
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Letts, IA
    Letts