Influenza is a common and contagious respiratory disease caused by influenza A, B, C, and D viruses (IAV, IBV, ICV, and IDV). A multiplex real-time RT-PCR assay was developed for simultaneous detection of IAV, IBV, ICV, and IDV. The assay was designed to target unique sequences in the matrix gene of IBV and ICV, the RNA polymerase subunit PB1 of IDV, and combined with USDA and CDC IAV assays, both target the matrix gene. The host 18S rRNA gene was included as an internal control. In silico analyses indicated high strain coverages: 97.9% for IBV, 99.5% for ICV, and 100% for IDV. Transcribed RNA, viral isolates and clinical samples were used for validation. The assay specifically detected target viruses without cross-reactivity, nor detection of other common pathogens. The limit of detection was approximately 30 copies for each viral RNA template, which was equivalent to a threshold cycle value of ~37.