Dark-billed Cuckoo has a very broad geographic distribution across South America, from the north end of South America in Venezuela and the Guianas to Peru, Bolivia, Paraguay, Argentina, Brazil; the Galapagos Islands, and Margarita Island; and reaching as far south as northern Argentina.
Dark-billed Cuckoo is partially migratory. It is resident west of the Andes in Colombia, Ecuador, and perhaps in Peru (Hilty and Brown 1986, Ridgely and Greenfield 2001a, Schulenberg et al. 2010). Southern populations (in southern Brazil, Uruguay, and Argentina) are present only during the austral summer (October to January or February) (Payne 1984); in much of the Amazon, however, it is present only during the austral winter (March-October) (Hilty and Brown 1986, Ridgely and Greenfield 2001a, Schulenberg et al. 2010). Breeds in the llanos of Venezuela (May-October), but is rare or absent there December-April (Hilty 2003).
Dark-billed Cuckoo primarily occurs in the lowlands, e.g. up to 950 m in Venezuela (Hilty 2003), but occasionally is reported up to 3600 m (Schulenberg et al. 2010).