| Library | 035 codes | 040 codes |
| Branford | br | brb |
| Durham | du | dur |
| East Lyme HS | eh | elh |
| East Lyme | el | ely |
| Essex | ex | esx |
| Guilford | gu | gui |
| Haddam | ha | had |
| Ivoryton | iv | ivy |
| Ledyard | lb lg | led |
| Madison | ma | mad |
| Mitchell | mc | mtc |
| Middletown | md | mdt |
| Meriden | me | mrd |
| North Branford | nb nt | nbr |
| North Haven | nh | nhv |
| New London | nl | nln |
| Norwich | nw | nwc |
| Old Lyme | ol | oly |
| Orange | or | org |
| Rathbun | ra | her |
| Stony Creek | st | stc |
| Wallingford | wa wb | wal |
| Woodbridge | wd | wbr |
| West Haven | wk wl wm wo | whm |
| Westbrook | ws | wsb |