Various people detection systems based on camera networks have been developed, and their services (output of users' locations) are utilized in a variety of applications. Usually, each application requires a people detection system to keep its quality-of-service (QoS) at a certain level. However, required system QoS levels vary widely among different applications, and the QoS requirements of each application range over various QoS factors, such as the coverage area, resolution, and frequency of users' locations. Moreover, the tradeoff between QoS factors arises from limitations on the system resources, which fluctuate due to changes in circumstances. Consequently, it is difficult for such systems to stably fulfill the diverse QoS requirements of individual applications. To deal with these difficulties, we propose a QoS control method for camera network based people detection systems. Taking into account the trade-off between several QoS factors under limited and varied system resources, our method dynamically adjusts system parameters and controls system QoS to provide each application with users' locations at a required QoS level. Experimental results indicate that our method well maintain system QoS for the changes in application requirements and system resources.