Complex sentence: The Censuses of 1901 and 1911 both offer a valuable insight into the population of the area at that time and it is noteworthy that a large proportion of the population are recorded as speaking both Irish and English as late as 1911.
Split into simpler sentences: The Censuses of 1901 and 1911 both offer a valuable insight into the population of the area at that time. Of note is that a large proportion of the population are recorded as speaking both Irish and English as late as 1911.