Conn. Gen. Stat. § 12-42

(b) If no declaration is filed, the assessor shall fill out a declaration including all property that the assessor has reason to believe is owned by the person for whom such declaration is prepared, liable to taxation, at the percentage of its actual valuation, as determined by the assessor in accordance with the provisions of sections 12-63 and 12-71 , from the best information the assessor can obtain, and add thereto twenty-five per cent of such assessment.

See Sec. 12-54 re assessors' examination of persons failing to return list of taxable property.

Irregularities in perfecting grand list. 30 C. 394. One giving in list estopped from claiming listed property is not taxable. 30 C. 398; 51 C. 259. Listing of real property against nonresident bankrupt corporation before assignment recorded here, good. 36 C. 283. Assessors having information sufficient to found honest belief may fill out list for negligent taxpayer. 54 C. 436. They may do so without learning of or specifying particular property. Id., 440; 58 C. 269. Under former law, nonresidents not liable to ten per cent addition. 56 C. 351; 89 C. 437. Effect of assessors' action in adding property. Id., 438. Reference to previous list is insufficient description. 103 C. 152. Where assessors make out list, property must be listed in separate parcels; mandamus lies to compel performance of such duty. 104 C. 546, 547. Owner's valuation not required. 108 C. 125. Burden is on property owner to furnish facts. 117 C. 393. Cited. 123 C. 546; 147 C. 262; 212 C. 167; Id., 639; 232 C. 335; 240 C. 192; Id., 422.