On 1 May 1851 the cantor Karl Herold founded a children's festival. On 23 June 1889 Sonnefeld and Hofstädten were merged as a single town under the name of Sonnefeld. In the same year, a war memorial was unveiled in the town square ("Marktplatz"), and the first railway line opened at Sonnefeld in 1901. During World War I, Sonnefeld had to surrender three church bells and the pipes of the church's organ to the war effort but they were replaced and dedicated in 1919 and 1924 respectively. On 1 June 1920, the dissolution of Saxe-Coburg and Gotha sent the district of Coburg, including Sonnefeld, to Bavaria. Before World War II, 1400 people were counted in Sonnefeld but in 1966 the population was down to 980 residents in 556 households. However, the subsequent additions, a total of 10 villages, to the municipality increased the population to 5,300.