Scotland a territorial parish structure, with every community in Scotland having a local congregation. Scotland also has a significant Roman Catholic population, 19% professing that faith, particularly in Greater Glasgow and the north-west. After the Reformation, Roman Catholicism in Scotland continued in the Highlands and some western islands like Uist and Barra, and it was strengthened during the 19th century by immigration from Ireland. Other Christian denominations in Scotland include the Free Church of Scotland, and various other Presbyterian offshoots. Scotland's third largest church is the Scottish Episcopal Church. Islam is the largest non-Christian religion (estimated at around 75,000, which is
Economy of Scotland in the Middle Ages written sources from which to re-construct the demography of Medieval Scotland. Estimates have been for the early period made of a population of 10,000 inhabitants in Dál Riata and 80–100,000 for Pictland, which was probably the largest region. From the formation of the Kingdom of Alba in the tenth century, to before the Black Death reached the country in 1349, estimates based on the amount of farmable land, suggest that population may have grown from half a million to a million. Although there is no reliable documentation on the impact of the plague, if the pattern followed that in England,