We demonstrate the detection of mid-wavelength (3-5 mum) infrared radiation by intersubband transitions in In(x)Ga1-xAs/Al0.45Ga0.55As multiple quantum well structures grown on GaAs substrates. The peak detector response is shifted from 4.8 to 4.3 mum by increasing the indium fraction from x = 0.05 to x = 0.20, while simultaneously decreasing the well width to keep the first excited eigenstate near the top of the wells. These detectors can be combined in detector stacks with conventional long-wavelength (8-12 mum) infrared quantum well detectors for multi-band imaging applications.