No. Illinois courts have consistently held that a joint deposit account is only created by the parties signing an explicit agreement to create a joint account. If both parties have not signed a joint account agreement or a signature card that creates a joint account, then the spouse who did not sign the account agreement or signature card is not a joint account holder. The Illinois Joint Tenancy Act also states that all parties to a joint account must sign the account agreement, either when the account is opened or sometime thereafter.