Exhibit 99.1

Mercantile Bank Corporation Reports Strong Third Quarter 2013 Results

Diluted earnings per share increased 33 percent

Asset quality continues to improve

GRAND RAPIDS, Mich., October 15, 2013 – Mercantile Bank Corporation (NASDAQ: MBWM) (“Mercantile”) reported net income attributable to common shares of $3.5 million, or $0.40 per diluted share, for the third quarter of 2013, compared with net income attributable to common shares of $2.6 million, or $0.30 per diluted share, for the prior-year period.

The third quarter was highlighted by:

“Mercantile’s very strong performance continued through the third quarter of 2013 as we continued to demonstrate leadership in our markets,” said Michael Price, Chairman and CEO of Mercantile. “Mercantile delivered strong operating results, improved financial strength and continued to build momentum in an improving regional economy. We continue to be encouraged by positive trends in new business development and remain confident that our year-to-date performance is indicative of the opportunities available to us over the remainder of 2013 and into 2014.”

Operating Results

Total revenue, which consists of net interest income and noninterest income, was $13.7 million during the third quarter of 2013, up slightly from the $13.6 million generated during the prior-year third quarter. The increase in total revenue during the 2013 period resulted from higher net interest income, which more than offset lower noninterest income. Net interest income during the third quarter of 2013 was $12.0 million, up $0.4 million or 3.5 percent from the third quarter of 2012, reflecting a 0.4 percent increase in average earning assets and a 9 basis point increase in the net interest margin. The net interest margin during the third quarter of 2013 was 3.76 percent, up from 3.67 percent during the comparable 2012 period.

Noninterest income during the third quarter of 2013 was $1.7 million, down 18.2 percent from $2.1 million during the prior-year third quarter. The decrease in noninterest income during the 2013 period primarily resulted from lower rental income on foreclosed properties and residential mortgage banking fee income.

Mercantile recorded a negative $1.7 million provision for loan losses during the third quarter of 2013 compared to a negative provision of $0.4 million for the third quarter of 2012. The negative provision expense is the result of several factors, including continued progress in loan recoveries and collections, a reduced level of loan-rating downgrades and ongoing loan-rating upgrades as the quality of the loan portfolio continues to improve. Loan recoveries totaled $2.0 million during the third quarter of 2013, while loan charge-offs not specifically reserved for in prior periods amounted to only $0.1 million, resulting in a net positive impact of $1.9 million on provision expense.

Noninterest expense totaled $9.9 million during the third quarter of 2013, down $0.3 million or 2.6 percent from the prior-year third quarter. Costs associated with the administration and resolution of problem assets, including legal expenses, property tax payments, appraisal costs and write-downs on foreclosed properties, totaled $0.4 million during the third quarter of 2013, down $1.2 million or 76.3 percent from the $1.6 million expensed during the third quarter of 2012. Gains on sales of other real estate, which are netted against problem asset costs, totaled $0.3 million during the third quarter of 2013. The reduction in problem asset costs reflects the continuation of Mercantile’s aggressive approach to managing and resolving problem assets. After-tax merger-related costs totaled $0.7 million for the quarter.

Mr. Price continued: “We were particularly pleased with the financial performance of our loan portfolio. We recorded a $1.7 million negative provision during the third quarter in large part due to $2.0 million in recoveries. We continue to prune our loan portfolio while taking advantage of new business opportunities in our region. We have the ability to be flexible and opportunistic as we pursue disciplined growth for long-term performance.”

Balance Sheet

As of September 30, 2013, total assets were $1.42 billion, down $0.9 million or 0.1 percent from December 31, 2012; total loans increased $34.3 million, or 3.3 percent, to $1.08 billion over the same time period. Compared to September 30, 2012, total assets grew $33.6 million, or 2.4 percent, and total loans grew $40.2 million, or 3.9 percent. Approximately $60 million in loans to new borrowers were originated during the third quarter as continuing relationship building efforts have led to increased lending opportunities.

Commercial-related real estate loans continue to comprise a majority of Mercantile’s loan portfolio, representing approximately 67 percent of total loans as of September 30, 2013. Non-owner occupied commercial real estate (“CRE”) loans, totaling $368 million or 34.2 percent of total loans as of September 30, 2013, increased $68.4 million or 22.9 percent during the last twelve months. Owner-occupied CRE loans, totaling $259 million or 24.1 percent of total loans at the end of the current year third quarter, declined $17.4 million or 6.3 percent since September 30, 2012. Commercial and industrial loans totaled $287 million or 26.7 percent of total loans as of September 30, 2013, up from $272 million or 26.3 percent of total loans as of September 30, 2012.

LOAN COMPOSITION

Mercantile has continued its efforts to improve liquidity by growing local deposits and reducing wholesale funding. As of September 30, 2013, total deposits were $1.12 billion, up $13.9 million from September 30, 2012. By comparison, local deposits increased $76.9 million to $904 million over the past year, representing 80.6 percent of total deposits compared to 74.7 percent at September 30, 2012. Growth in local deposits was driven primarily by new commercial relationships, the introduction of innovative new products, various deposit-gathering initiatives and enhanced advertising and branding campaigns.

Wholesale funds were $262 million, or 21.3 percent of total funds, as of September 30, 2013, compared to $305 million, or 24.7 percent of total funds, as of December 31, 2012, and $315 million, or 26.2 percent of total funds, as of September 30, 2012.

Short-term investments, consisting of federal funds sold and interest-bearing bank deposits, averaged $65.9 million during the third quarter of 2013. In addition to its short-term investments, Mercantile had approximately $147 million of borrowing capacity through various established lines of credit to meet potential funding needs, as well as approximately $38 million of unpledged U.S. Government securities as of September 30, 2013.

Asset Quality

Nonperforming assets (“NPAs”) at September 30, 2013 were $12.2 million, or 0.9 percent of total assets, compared to $25.9 million as of December 31, 2012, and $35.9 million as of September 30, 2012 (1.8 percent and 2.6 percent of total assets, respectively). This represents a reduction of $13.7 million or 53.1 percent from the end of 2012, and a decline of $23.7 million or 66.2 percent from the year-ago quarter-end.

Robert B. Kaminski, Jr., Mercantile’s Executive Vice President and Chief Operating Officer, noted: “We remain pleased with our ongoing success in improving asset quality and the dramatic decline in nonperforming assets over the past several years. The actions taken over the past several years reflect our aggressive stance to move troubled assets off our balance sheet. Nonperforming assets now represent only 0.9 percent of our total assets and our 30-to 89-day delinquent loans continue at a nominal level. We are grateful to the entire Mercantile team for all their hard work on this initiative, while staying true to our community banking roots, maintaining a steady focus on meeting the needs of our existing customers and driving the growth of new relationships in our markets. While our markets remain competitive, we believe we are benefiting from our robust sales programs and marketing initiatives and the overall value that Mercantile brings to clients as evidenced by the $74 million in loans to new borrowers we originated in the third quarter.”

Nonperforming loans (“NPLs”) totaled $8.6 million as of September 30, 2013, down $1.9 million and $16.2 million, respectively, from the linked quarter-end and the year-ago quarter-end, while foreclosed real estate and repossessed assets declined $0.4 million and $7.6 million, respectively, from the linked and year-ago quarter-ends. CRE loans represented 46.1 percent of NPLs, or $4.0 million at September 30, 2013. Investor-owned nonperforming CRE loans accounted for $3.3 million of total CRE NPLs, while owner-occupied CRE NPLs accounted for $0.7 million. Owner-occupied and rental residential NPLs totaled $2.9 million or 33.2 percent of total NPLs as of September 30, 2013.

NONPERFORMING ASSETS

During the third quarter of 2013, Mercantile added only $0.9 million of NPAs to its problem asset portfolio, while disposing of $3.2 million through a combination of principal payments and asset sales ($2.9 million), loan charge-offs ($0.1 million), and foreclosed asset valuation write-downs ($0.2 million). In total, NPAs decreased by a net $2.3 million, or 15.8 percent, during the third quarter of 2013.

NONPERFORMING ASSETS RECONCILIATION

Net loan recoveries were $1.9 million during the third quarter of 2013, or an annualized negative 0.7 percent of average loans, compared with net loan recoveries of $0.4 million (negative 0.2 percent annualized) and net loan charge-offs of $1.5 million (0.6 percent annualized) for the linked and prior-year quarters, respectively.

NET LOAN CHARGE-OFFS (RECOVERIES)

Capital Position

Shareholders’ equity totaled $150 million as of September 30, 2013, an increase of $3.2 million from year-end 2012. The Bank remains “well-capitalized” with a total risk-based capital ratio of 15.3 percent as of September 30, 2013, compared to 14.7 percent at December 31, 2012. At September 30, 2013, the Bank had approximately $64 million in excess of the 10.0 percent minimum regulatory threshold required to be considered a “well-capitalized” institution. Mercantile reported 8,707,534 total shares outstanding at September 30, 2013.

Reflecting the continued strength of Mercantile’s operating performance and capital position, on October 10, 2013, the Board of Directors declared a fourth quarter cash dividend of $0.12 per common share, which is payable on December 10, 2013 to shareholders of record on November 8, 2013.

Mr. Price concluded: “As we work to consummate our merger of equals with Firstbank Corporation, we continue to make steady progress within the current Mercantile franchise. We believe that this business combination will bring together two very strong community banks to create a major Michigan financial institution. We continue to be a premier community bank with strong customer relationships and a growing pipeline of new business opportunities. The ongoing recovery in the Michigan economy is an additional tailwind for our business. We are optimistic about our ability to create a combined business enterprise that can deliver disciplined growth and increasing value to our shareholders based on steady improvement in financial performance, a strong capital position and new market opportunities in western and central Michigan.”

About Mercantile Bank Corporation

Based in Grand Rapids, Michigan, Mercantile Bank Corporation is the bank holding company for Mercantile Bank of Michigan. Founded in 1997 to provide banking services to businesses, individuals and governmental units, the Bank differentiates itself on the basis of service quality and the expertise of its banking staff. Mercantile has seven full-service banking offices in Grand Rapids, Holland and Lansing, Michigan. Mercantile Bank Corporation’s common stock is listed on the NASDAQ Global Select Market under the symbol “MBWM.”

Forward-Looking Statements

This news release contains comments or information that constitute forward-looking statements (within the meaning of the Private Securities Litigation Reform Act of 1995) that are based on current expectations that involve a number of risks and uncertainties. Actual results may differ materially from the results expressed in forward-looking statements. Factors that might cause such a difference include changes in interest rates and interest rate relationships; demand for products and services; the degree of competition by traditional and nontraditional competitors; changes in banking regulation or actions by bank regulators; changes in tax laws; changes in prices, levies, and assessments; the impact of technological advances; governmental and regulatory policy changes; the outcomes of contingencies; trends in customer behavior as well as their ability to repay loans; changes in local real estate values; changes in the national and local economies; and other factors, including risk factors, disclosed from time to time in filings made by Mercantile with the Securities and Exchange Commission. Mercantile undertakes no obligation to update or clarify forward-looking statements, whether as a result of new information, future events or otherwise.

FOR FURTHER INFORMATION:

AT MERCANTILE BANK CORPORATION:

Mercantile Bank Corporation

Third Quarter 2013 Results

MERCANTILE BANK CORPORATION

CONSOLIDATED BALANCE SHEETS

Mercantile Bank Corporation

Third Quarter 2013 Results

MERCANTILE BANK CORPORATION

CONSOLIDATED REPORTS OF OPERATIONS

Mercantile Bank Corporation

Third Quarter 2013 Results

MERCANTILE BANK CORPORATION

CONSOLIDATED FINANCIAL HIGHLIGHTS

(Unaudited)