Higher net interest income helped push First of Long Island Corp.’s fourth quarter profit up by 21 percent from a year earlier.

The Glen Head-based holding company for the 43-branch First National Bank of Long Island said Monday its net income for the three months ended Dec. 31 was $6.6 million or 46 cents a share, up from $5.5 million or 39 cents a share in the quarter a year earlier.

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The bank credited an 18 percent increase in net interest income, to $20.4 million, plus net gains on the sale of securities of $191,000 and a decrease of $274,000 in expenses, including real estate taxes, depreciation, upkeep of buildings, rent, utilities, insurance and other items.

Total assets at Dec. 31 were $3.1 billion, up 15 percent from a year earlier.