Most modern Catholic churches are designed without acoustic solutions, and good acoustics are often a matter of chance. Therefore, it is essential to address the subject of architectural acoustics of religious buildings. The paper presents the acoustic design of Church of Our Lady of Fatima in Koziegłowy, which has a volume of 8,000 m³ and was inaugurated in 2022. The entire design process aiming at achieving optimal acoustic conditions was presented. Acoustic investigations in the interior were carried out during different stages of work. The paper shows how the church’s acoustics changed at each construction stage until the completion, where acoustic parameters were obtained following the recommendations. The assessed acoustic parameters include Reverberation Time (RT), Early Decay Time (EDT), Clarity (C80) and (C50), Definition (D50) and Speech Transmission Index (STI). Additionally, the acoustic properties of the church were compared with other churches of similar volume built in the last twenty years.