Complex sentence: By 1980, the population had grown increased to 4,091, to 4,756 by 1990 and, then jumped to 6,973 in the year 2000 census.
Split into simpler sentences: By 1980, the population had grown to 4,091 and to 4,756 by 1990. The population then jumped to 6,973 in the year 2000 census.