Be certain you're looking at the Assessed value and not just the Market value. You're taxed on the Assessed value. If your neighbors are being taxed on substatially lesser assessed values than you are (similar houses), then you can pull together some "comparables" to document your protest at the Assessor's Office. To the best of my knowledge, the 10% rule is statewide. It would be interesting to know how the Assessor learned what you paid for the house, as that's not public information in Texas.