Mycobacterium avium subsp. paratuberculosis (MAP) was first reported in the endangered Key deer (Odocoileus virginianus clavium) in 1996 on Big Pine Key, Florida, USA. By 2008, eight additional MAP-positive Key deer had been identified on Big Pine Key and the nearby Newfound Harbor Keys. This study was conducted to determine if MAP was still present in Key deer and whether natural or man-made freshwater sources were contaminated with MAP. Between November 2009 and September 2012, MAP was isolated from 36/369 (10%) fecal samples collected from the ground throughout the Key deer range on Big Pine Key and the Newfound Harbor Keys, but all 36 positive samples were from Little Palm Island (36/142 [25%]). Only 1/729 (0.1%) environmental samples was positive; this was from the garden fountain on Little Palm Island (1/81 [1%]). In addition, MAP was detected in 3/43 (7%) necropsied Key deer, all from Little Palm Island (3/3 [100%]). Of these three Key deer, pooled samples from the ileum, cecum, and ileocecal lymph node from two were MAP-culture positive and feces from one of these were culture-positive. The third deer was only PCR-positive. Evidence of MAP was only detected on Little Palm Island during this sampling period and environmental contamination was limited.