Suffolk Bancorp, parent of the Suffolk County National Bank, said its first quarter net income rose by almost 21 percent over a year earlier on higher net interest income.

The Riverhead-based 27-branch bank holding company said it earned $4.8 million or 41 cents a share in the three months ended March 31. Per share earnings in the year earlier quarter were 34 cents.

The company said total loans outstanding increased by 26.5 percent from the year earlier quarter, to $1.75 billion.

“The quarter’s loan growth reflected strong performance by lending teams situated in both our traditional markets in Suffolk County, as well as our expansion markets in Nassau County and New York City,” president and Chief Executive Howard Bluver said in a statement.

Net interest income rose by 10.9 percent, to $18.3 million in the first quarter from a year earlier, although the gain was partly offset by increased operating expenses, a higher effective tax rate and a drop in noninterest income because of a onetime gain in the year-earlier quarter from the sale of loans.

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Suffolk had total assets of $2.3 billion at March 31, a gain of 21 percent from a year earlier.

The bank’s shares dropped 71 cents Thursday to close at $23.91.