The study also found that, on average, a U.S. Immigration and Customs Enforcement hold leads to an extension of a person's stay in jail by nearly 30 days when compared with a person without an immigration detainer.
Researchers also said that four in five people put on hold have never been convicted of a crime against a person in Washington state and a similar ratio had never been convicted of a felony. Another result was that immigration holds affect Latino communities acutely with more than a quarter of detainers being a Latino person.
The study, led by sociology professor Katherine Beckett, analyzed booking data from 2011. It was commissioned by the Northwest Defenders Association.
The study analyzes data from 2011, a year before the federal program known as Secure Communities went into effect in the county. The federal immigrant jail check program uses fingerprint analysis to identify illegal immigrants in county jails.
In King County, the use of fingerprints began in 2012. Immigration agents also comb jail rosters to look for people who were born abroad, among other monitoring techniques.
Secure Communities has been rolled out nationwide despite pushback from several states, counties and cities in the past couple of years.
Immigrant right groups say Secure Communities can discourage immigrants from reporting crimes and can lead to the deportation of people who haven't been convicted of anything.
In Seattle, immigrant rights and domestic violence groups have lobbied King County executive Dow Constantine and the County Council to halt honoring a key component of the program. In February, Constantine wrote a letter to the council saying that he supports narrowing honoring detainers for serious crimes.
Other counties and cities - including New York City; San Francisco County in California and Cook County in Illinois - have announced that they will honor ICE detainers only if certain conditions are met. In California, Attorney General Kamala Harris said in December that Secure Communities remains a "flawed" program because nearly one-third of the people targeted by the requests there have never been convicted of a crime.
A U.S. Immigration and Customs Enforcement spokesman declined to comment.
In December, ICE further tweaked the guidelines for detainers, saying that ICE agents should ask for holds for people who have three or more prior misdemeanors. People with felony convictions and charges should also be held. ICE also has put drunken driving charges under its priority list.
Among other findings: about one-eighth of people under a detainer had not been charged with a crime prior to a transfer to ICE; for just over half of the people flagged by ICE, the most serious crime was a misdemeanor.
Municipalities can ask for federal reimbursement for costs of holding suspected illegal immigrants. In fiscal year 2012, King County got nearly $725,000, but reimbursement fluctuates and the budget has been slashed from $240 million to $70 million.
Beckett also said holds have a domino effect on the jail system. The holds shape decisions by prosecutors, judges and defendants. For example, a person may not post bail because they know they will be held by ICE, keeping them in custody longer. Or if the person knows deportation is a possibility, they delay seeking release to make arrangements with their families in preparation for removal.
"So it's not that people are being held longer than the rules allow, but rather that their decisions about the criminal matter are affected by the presence of a detainer," Beckett said.