Washington - The US prison population increased by more than 61,000 inmates last year to a record of nearly 1.25 million state and federal prisoners, the US Justice Department reported yesterday. The department's Bureau of Justice Statistics said the increase in the nation's adult prison population was 5.2 per cent in 1997, slightly lower than the average annual growth rate of 7 per cent earlier in the 1990s. During the last seven years, the nation's prison population has soared by more than 60 per cent, increasing by more than 470,000 inmates.