The number of Americans under the supervision of state adult correctional systems has fallen to the lowest level in a decade, the federal government said Tuesday, while the number of people serving time in federal prison fell for the first time in more than three decades.

Data from the Bureau of Justice Statistics showed that 6,899,000 adults were under supervision of various adult correctional systems at the end of 2013, the last year for which figures are available. The number of adults under supervision includes those who are incarcerated, on parole or on probation.

The total number declined by 41,500 from the end of 2012, and it represented the first time since 2003 that the number fell below 6.9 million. About one in every 35 adults was under some form of correctional supervision at the end of 2013, unchanged from the previous year. That rate is the lowest it has been since 1997. The total incarceration rate has fallen, too, from about one in every 100 adults to one in every 110 adults.

Maine had the lowest rate in the country at the end of 2013, with just 980 adults per 100,000 under some form of supervision.

Adam Gelb, director of the Public Safety Performance Project at the Pew Charitable Trusts, called that decline significant. States have reported an uptick in the number of inmates they hold this year, although further reforms to the criminal justice system could lower those numbers over the long term.

The drop in prison populations came almost entirely from declines in the number of adults under community supervision and the number of inmates housed in local jails. At the end of 2013, 2,220,000 inmates were being housed in prisons or jails, down 11,000 from the year before.

And 2013 marked the sixth consecutive year that the number of supervised adults had decreased, since reaching a peak in 2007. Still, prison populations remain near an all-time high: More than 1.5 million inmates are housed in state or federal prisons, and another 731,000 are in local jails. The local jail population fell by 13,000 inmates from the previous year.

The total prison and jail populations have increased 1.2 percent per year since 2000, the bureau reported, although it reported declines over the last six years. The federal prison population has led the growth, rising from almost 134,000 in 2000 to 205,700 today, while state prison populations have grown by a much smaller percentage.

Texas houses the highest number of prisoners in state prisons and local jails, at 221,800. California, at 218,800 inmates, is close behind. But Georgia has the highest number of residents under some form of supervision, with 536,200 residents on probation or parole. Combined with the 91,600 inmates in Georgia’s state and local prison and jail system, that means 8,290 out of every 100,000 Georgia adults are under some form of supervision by the state, far higher than any other state.

As prison populations spiked in the 1990s and 2000s, states have had to shell out billions to pay for infrastructure and housing costs. In recent years, those states have begun experimenting with new ways to reduce crime rates and the number of inmates who make their way into the system.

In Texas, a series of reforms implemented seven years ago has reversed the explosive growth of the inmate population. To counter the huge number of former inmates who returned to jail after violating parole, the state implemented reforms in 2007 that created hundreds of new beds in drug treatment programs with names like the In-Prison Therapeutic Treatment and Substance Abuse Felony Punishment Facilities.

Some probation violators could be sent to intermediate sanction facilities, a step lower than prison, aimed at getting an offender’s attention without locking them up. More slots were set aside in outpatient treatment programs for criminals sentenced to probation.

Pre-trial diversion programs for those suffering from mental illnesses, overseen by officers who specialize in mental health and drug treatment, helped more people avoid jail.

The reforms have saved the state at least $3 billion to date, according to some estimates.

But reform advocates say there is much more states could do to cut their prison populations, including reforming sentencing guidelines they say put criminals away far longer than their crimes deserve.

“The prison population is determined by two things: How many people go in the front door, and how long they stay,” said Michele Deitch, a senior lecturer at the Lyndon Baines Johnson School of Public Affairs at the University of Texas. “I think we need to be asking ourselves why we still feel this pull toward incredibly long sentences.”