Up the river

The maximum security Sing Sing Prison was built in Ossining, New York in 1828, approximately 30 miles 'up the [Hudson] river' from New York City.

Hence a felon convicted of a crime in New York City from 1828 on might be sent 'up the river' to serve his time at Sing Sing.

Sing Sing Prison 1855

Being sent up the river has since come to mean serving time in any prison.

("Down the river' on the other hand comes from the days of the American slave trade when troublesome slaves might be sold 'down the [Mississippi] river' to cotton plantations in the Deep South.)

Sarge D