Pam, This often happens in our rural Tennessee area when you have finished a basement or added on to the home and the county tax assessor has not changed the county records. If you are listing your home for sale, you need to have it corrected. Correcting it will probably raise your taxes. A local REALTORÂ® can help you. If you are selling by yourself, call the county assessor's office for assistance. You could be accused of fraud by not revealing this to a prospective buyer.
On Trulia it says that the information is from the Assessor, which would be from tax records. I looked at your tax record and it shows your first story to have 1288 sq. ft.. Your information is more than likely coming from that. If you have claimed your home then you should be able to make changes to it.
Keep in mind that online information is often fed in from multiple sources, and if the information is not corrected from the originating source, errors may appear--if you are currently listed with an agent, he/she should be able to make any corrections needed, just ask--or consider contacting Trulia's customer service department directly--under the help tab.