In a major turnaround, Jackson Health System finished in the black for the fiscal year that ended Sept. 30, the chief financial officer said Thursday.

After losing $419 million the previous three years, Mark Knight said year-end financial adjustments mean Jackson, the safety net hospital for Miami-Dade County’s poor and uninsured, will show a slight surplus for the year.

That “cleanup,” as Knight called it, gave a major last-minute bump to the system’s finances. Just last month, Jackson’s financial statements projected a year-end loss of $14.4 million.

Knight refused to give an exact figure for the surplus, saying the September monthly report won’t be finalized until next week, but he said the financial shift represents a “significant turnaround” from the $81 million Jackson lost in fiscal 2011.

Monday’s good news came after five years of massive struggles for the public hospital system. Last year, the situation was so dire that a Boston for-profit hospital system offered to take over Jackson to protect the county government from having to pay Jackson’s bills if the hospitals couldn’t meet payroll.

Commissioners flatly turned down that offer and appointed a career banker, Carlos Migoya, who took over in May 2011, vowing to turn Jackson around quickly.

The last year Jackson finished unquestionably in the black was 2006, when it showed a surplus of $57 million. In 2008, the system finished with a surplus of $25 million — but a later audit showed that figure was a major miscalculation of the system’s true finances, leading to adjustments that ended in an audited loss of $244 million in 2009.

Knight attributed this year’s change to reining in expenses and laying off 920 full-time workers last spring while hiring about 350 part-timers to create a flexible work force that could adjust to varying patient volumes.

Another major factor was a massive restructuring of the JMH Health Plan. The plan, which lost $26.5 million last year, finished with a surplus of $18.1 million, after drastic measures such as removing Jackson employees from the plan and closing down the plan’s Medicaid operations.

Still, Knight told the Jackson board Thursday that September ended with only 13 days of cash on hand — far below the 300 days that the prosperous Memorial Healthcare System in South Broward, another public system, has in reserve.

Because of Jackson’s precariously low figure, the board on Thursday approved a plan to obtain a $75 million revolving line of credit from Wells Fargo.

Chief Executive Migoya said the line of credit will allow smooth operations if there are any “hiccups” in cash flow and would help Jackson save money by getting discounts from some vendors for fast bill payment.

Migoya noted to the board that he had retired from Wells Fargo, after previously working for Wachovia, which Wells Fargo bought. Migoya said the deal was negotiated by his staff with Wells Fargo employees who “used to work with and for me,” but that Wells Fargo was the county’s and Jackson’s bank without any influence from him.

The funds will be available at an interest rate of 1.175 percent, Migoya said.

Board member Michael Bileca, an accountant and state legislator, said he was “slightly uncomfortable” with the line of credit because he was concerned it might make administrators less focused on operating Jackson efficiently.