THE NUMBER OF DEATHS in Massachusetts from COVID-19 shot up by 37 percent Tuesday, prompting questions about why some parts of the state are being impacted more severely than others.

The death toll from COVID-19 reached 356, up from 260 on Monday.  Officials say the latest numbers include some deaths from over the weekend. The number of confirmed COVID-19 cases rose a fairly modest 10 percent to 15,202. A surge in COVID-19 hospitalization is expected later this week.

State officials break down COVID-19 infections and deaths by county. Middlesex has the most deaths so far at 69, but it’s also the county with the largest population at nearly 1.6 million. Worcester County, second in population size with 822,000 people, has 24 deaths, and Bristol County, sixth in population size, has 16.

Three smaller counties have a disproportionately large number of the state’s deaths. Hampden County, eighth in population with 469,000 people, has the second-most deaths at 57. Berkshire and Franklin, two of the state’s smallest counties in terms of population, have 18 and 17 deaths, respectively.

Franklin, Berkshire, and Hampden have by far the most deaths per 1,000 residents. Franklin is tops in Massachusetts with .24 deaths per 1,000 residents, Berkshire is second at .14, and Hampden is third at .12. No other county in Massachusetts comes close.

In New York City, which many consider the epicenter of the COVID-19 outbreak in the United States, the number of deaths rose by 806 on Tuesday to 3,544. New York City had .41 deaths per 1,000 residents.

Alarmed by the numbers in Massachusetts, five lawmakers from the western part of the state have asked the Baker administration for an explanation of why Franklin County has so many deaths per 1,000 residents.

Marylou Sudders, the governor’s secretary of health and human services, said at a press conference with Baker on Tuesday that her office is taking a deeper dive into the data to better understand what’s going on in specific counties. She also said she wants to see if COVID-19 is impacting different ethnic groups differently, as has been reported elsewhere. She said she intends to release whatever data the state has, but indicated it’s full of holes because key information on race and ethnicity is often left blank.

Early indications are that clusters of deaths at nursing homes in the three communities may be distorting the county-by-county data. In Berkshire County, at least 10 deaths have occurred at Williamstown Commons in Williamstown and more residents there and at Fairview Commons in Great Barrington have reportedly tested positive for COVID-19.

In Franklin County, two nursing homes in Greenfield have had a number of residents test positive for COVID-19 and some have died. Sen. Adam Hinds of Pittsfield said he heard there were four deaths at each of the facilities.

Hampden County’s fatality numbers have been driven up by the spread of COVID-19 through the Holyoke Soldiers’ Home, where 25 deaths have been reported so far.

Sudders said she had a breakdown of deaths in nursing homes across the state, but her office couldn’t provide it last night. The daily report from the state Department of Public Health doesn’t track nursing home deaths. The Tuesday edition reported that 958 residents and/or workers at 129 of the state’s long-term care facilities have tested positive for COVID-19.

House Speaker Robert DeLeo and Rep. Ruth Balser of Newton filed legislation on Tuesday requiring all long-term care facilities in the state to report to the Department of Public Health the number of positive tests and deaths in their facilities on a daily basis. The bill requires the state agency to report the information to the Legislature on a weekly basis.

“As we confront this public health emergency, we need prompt information on how COVID-19 affects those in our long-term care facilities,” DeLeo said in a statement.

Balser, in a phone interview, said the bill was prompted by the apparent failure of officials at the Holyoke Soldiers’ Home to alert state officials to the spread of the disease at the facility. Balser said she assumes most facilities are reporting that type of information to the state. “That is happening a lot,” she said. “We want to make sure it happens consistently.”

Three western Massachusetts lawmakers sent a letter to Sudders on Tuesday asking for more detailed information on the spread of COVID-19 in each county. They said local communities are releasing information in a way that leads to confusion. They urged the secretary to gather and release data on a weekly basis showing in which towns deaths occurred in each county and the gender, age, race, and ethnicity of each of the victims.

“We are interested in reviewing this data to better recognize gaps in care, disparities across regions, and variances in the number of coronavirus test locations across the Commonwealth,” they said.

Hinds said he is not convinced that the numbers are higher in the western Massachusetts counties just because of isolated clusters of deaths at long-term care facilities. He said Berkshire and Franklin have populations that trend older than the rest of the state and tend to be in poorer health with fewer financial resources. He also pointed out that nursing homes are scattered around the state, yet the clusters seem to be isolated in certain areas.

“I’m still concerned,” he said. “There’s a range of factors we’re trying to get at.”