The Collaborative International Dictionary of English v.0.48:

Untilled \Untilled\
   See tilled.

WordNet (r) 3.0 (2006):

untilled
    adj 1: not plowed or harrowed or hoed; "untilled land"

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "untilled":
   acarpous, arid, barren, celibate, childless, desert, desolate,
   drained, dried-up, dry, exhausted, fallow, fruitless, gaunt,
   gelded, impotent, ineffectual, infecund, infertile, issueless,
   jejune, leached, menopausal, nonfertile, nonproducing,
   nonproductive, nonprolific, sine prole, sterile, sucked dry,
   teemless, uncultivated, unfertile, unfruitful, unplowed,
   unproductive, unprolific, unsown, virgin, waste, wasted,
   without issue