Thirlmere, a small semi-rural town in the Macarthur Region of New South Wales, Australia, has a history closely linked to the development of rail transport in the region. Originally named after Thirlmere in England, Thirlmere's development significantly accelerated with the creation of the Great Southern Railway between 1863 and 1867. During this period, the area was bustling with railway workers, and temporary tent cities were established to accommodate them. Thirlmere was particularly valued for its proximity to the Thirlmere Lakes, which were then known as Picton Lakes, providing essential water for steam trains.

The town underwent significant changes with the deviation of the Thirlmere section of the Main Southern Railway in 1919 to a less steep alignment with easier grades. This deviation transformed Thirlmere from a hub of steam train activity to a quieter farming region, mainly supplying food and goods to the surrounding villages.

Thirlmere has been a significant settlement for Estonian immigrants, especially after the Second World War. Many Estonians fled to Australia to avoid being sent to Siberia by the Soviet regime. These immigrants played a crucial role in developing the successful poultry industry in Thirlmere, which at one point was the largest egg producer in the state and still contributes significantly to NSW's poultry produce.

The town has maintained its railway heritage and is home to the NSW Rail Museum, which boasts an extensive collection of railway exhibits. Thirlmere Lakes National Park, another key attraction, offers a serene environment with opportunities for picnics, kayaking, and birdwatching. The park is also home to diverse wildlife, including platypuses and wombats.