Checking account routing numbers are on the bottoms of checks and deposit slips, explains About.com. They are nine digits long and are the first series of numbers on a check or deposit slip.
The next series of numbers on a check or deposit slip constitutes the account number, according to About.com. The initial four digits of a checking routing number indicate where the bank is physically, although bank mergers and other changes mean that often, no correlation exists between those numbers and the location of the bank. Digits five and six signify which Federal Reserve bank any transfers go through, and the seventh digit indicates which Federal Reserve check processing center initially worked with the bank. Digit eight signifies the bank's Federal Reserve district, and the ninth digit is a check sum number to ensure the validity and legality of the routing number.