This spread of English into the religious lives of the Cornish people is seen as one of the main factors in the demise of Cornish as the common language of the Cornish people. As the Cornish language disappeared, so the people of Cornwall underwent a process of English assimilation.

The Cornish language (Kernowek) went extinct as a "living community language" in the late 18th century, with the death of Dolly Pentreath in 1777 often cited as the symbolic end. The decline was caused by several centuries of economic and social pressure from English. Following the Prayer Book Rebellion of 1549, the English government actively suppressed non-English services, and as Cornwall became more integrated into the British economy through mining and trade, English became the language of upward mobility. By the 1700s, Cornish was relegated to isolated fishing villages and eventually faded away as the older generation died out. However, in 2026, it is important to note that Cornish is no longer considered "extinct" by UNESCO but rather "critically endangered." A successful revival movement in the 20th and 21st centuries has led to a new generation of fluent speakers, bilingual road signs in Cornwall, and legal recognition under the European Charter for Regional or Minority Languages.