Social Security Numbers that start with 521-XX-XXXX are assigned to Colorado.
"Group Number" refers to the middle two digits of a Social Security Number. Group numbers are assinged on a
demand basis in the following order.
ODD Numbers 01-09
Even Numbers 10-98
Even Numbers 02-08
ODD Numbers 11-99
Listed below is every Active group number that starts with 521. Any number not listed is most
likely an invalid number.
If you need more detailed information about a social security number, enter a full nine digit number into
the search bar above to obtain instant results.