This paper presents a comprehensive exploration of the properties, principles, design methodologies and practical applications of Butterworth filters. The Butterworth filters are acknowledged for their flat frequency response in the passband, which is at a maximal level, while introducing minimal distortion to the signal of interest. Therefore, they were commonly applied in various situations. The study centers on a detailed investigation of a specific case involving the analysis of a third-order Butterworth lowpass filter circuit using Sallen-Key circuit topology. The Sallen-Key topology was basically utilized to achieve the Butterworth filter in the second-order circuit design. Moreover, in order to complete the third-order Butterworth filter design, an additional circuit part was also established apart from the second-order Butterworth filter. The simulation of the circuit was done in the software LTspice. This article will provide an overview of the research, discussing the essential characteristics of Butterworth filters and their significance in signal processing. The findings of this study contribute to a deeper understanding of Butterworth filters and their role in various signal processing applications.