The first major data release from the 2020 census shows Honolulu’s population topping the 1 million mark for the first time — likely no surprise to residents who travel Oahu’s busy roads and compete for housing, parking and public spaces.

To be more precise, the results of last year’s census — the first to allow households to respond to the decennial survey online — set Honolulu’s population at 1,016,508, up 6.6% from an influx of 63,301 residents since 2010, according to data released Thursday.

The state as a whole experienced a 7% population increase from the last census, with 1,455,271 people counted, including 94,970 new residents over the 10-year period.

Nationally, Hawaii ranked as the 40th most populous state, unchanged from 2010, and 35th in terms of numerical population change and 23rd in percentage change.

The new census data also showed only slight percentage changes among the state’s racial and ethnic populations from the 2010 census, with Asians and whites comprising the two largest groups in Hawaii’s melting pot, at 36.5% and 21.6%, respectively.

While that represents a slight share decline for both groups, Native Hawaiians and other Pacific Islanders increased their representation to 10.2% from 9.4% in 2010.

Both the increase in Honolulu residents and slower-than-projected growth on the neighbor islands were unexpected, considering recent population estimates, according to chief state economist Eugene Tian with the Department of Business, Economic Development and Tourism.

“The neighbor islands are not growing as fast as we thought, and Oahu is not growing as slow as we thought. These results show Honolulu County is actually increasing faster than Maui — that was a surprise,” said Tian, who was still poring over the data Thursday.

In the years immediately after the 2010 census, state population estimates for Honolulu steadily increased, hitting a high of 992,268 in 2016 before a three-year slide to an estimated 974,563 in 2019. Honolulu was the only county to see a decline in its estimated population during the 10-year stretch.

Tian said state officials had projected Honolulu’s 2020 population at approximately 1.01 million, about 6,500 fewer residents than the newest census tally. Meanwhile, the state population projection of 173,000 for Maui County exceeded the actual 2020 census figure by about 8,200 residents.

Kauai and Hawaii counties saw the largest percentage of population growth among the four major counties, at 9.3% and 8.4%, respectively. Kauai’s population was pegged at 73,298, an increase of 6,207 over the 10-year period, according to the census data. Hawaii County’s population hit 200,629, with 15,550 new residents.

With a population density of 49.8 people per square mile in Hawaii County and 118.2 per square mile on Kauai — compared with 1,692.4 people per square mile on Oahu — perhaps it’s not hard to see the attraction.

Maui County’s population increased 6.4% to 164,754, with 9,920 new residents since 2010 and a population density of 141.8 people per square mile.

Tian said he hasn’t had time to thoroughly analyze the newly released data to uncover an explanation for the surprising results or discern who the new Hawaii residents are and where they came from.

One reason for Oahu’s higher-than-expected population might be that Honolulu usually has a better census response rate than the other counties, he said.

Tian said “Oahu is doing good,” since a growing population is necessary to expand and sustain the economy by providing an adequate labor force, capital for infrastructure and technology, and greater consumer demand.

But it also can drive up the demand for housing, he said, and with it, the cost of living.

It’s no surprise that Hawaii once again was the most ethnically diverse state in the country, topping the U.S. Census Bureau’s “diversity index,” which measures the probability that two people chosen at random will be from different race and ethnicity groups.

Hawaii led the index with a 76% probability, with California in the second spot at 69.7%.

Hawaii also was the only state with Asians comprising the largest racial or ethnic group, according to the census data. Whites were the second-largest group, followed by those identifying as “two or more races,” also referred to as multiracial.

Whites made up the largest racial or ethnic group in three of the state’s four major counties: Hawaii (32.2%), Maui (31.5%) and Kauai (30.3%). In Honolulu, Asians accounted for 42.2% of residents, followed by multiracial (19.5%) and whites (17.3%).

Although still the most prevalent groups when considering the statewide population, the 2020 census indicated a decline of roughly 1 percentage point for both Asians and whites from 2010, even as their numbers increased, with a slightly higher percentage of residents identifying as multiracial.

Along with Native Hawaiians and other Pacific Islanders, Hispanics or Latinos also registered an increasing share of Hawaii’s population at 9.5%, up from 8.9% in 2010. The percentage of multiracial residents increased from 19.4% in 2010 to 20.1% in 2020, according to the census data.

The percentage of Blacks or African Americans was steady at 1.5% in both counts.

The 2020 census results revealed that Hawaii had the highest “diffusion score” in the nation at 21.8%, followed by Alaska (17.9%), Oklahoma (17.8%) and Nevada (16%). The diffusion score measures the percentage of residents not in the three largest groups combined, so the higher the score, the less concentrated the population is in the most prevalent groups.

In terms of housing, Hawaii joined Connecticut, Delaware, Massachusetts, New Jersey and Rhode Island as the only states with more housing units in 2020 than in 2010 in every one of their counties. The 2020 data counted 561,066 housing units statewide, up 8% from 2010.

Other census data indicated an increase in Hawaii’s adult population, with 79.4% of residents age 18 and older, up 9.4% from the previous census.

Hawaii ranked 13th in terms of percentage of adult population. Nationally, the figure was 77.9%, up 10.1% from the 2010 census.

The U.S. Census Bureau said more 2020 population results will be available at a later date, including statistics on age, sex, race and ethnicity.

The U.S. decennial census is used to determine the number of seats each state will have in the U.S. House of Representatives for the next 10 years based on the population — Hawaii’s remains at two — and helps determine how billions in federal funding is distributed to states and counties.

Tian said the population data is also vital for decision-making on the state and county levels, guiding planning over the next 10 years.

“It has a lot of implications, for housing demand, infrastructure, retail development, transportation, energy planning — all these things will be based on the new data. Even our economic forecasts and population estimates will be based on the 2020 census,” he said.