United States President Joe Biden will honour Emmett Till, the Black teenager whose 1955 killing helped galvanise the Civil Rights movement, and his mother with a national monument across two states.

Tuesday marks the 82nd anniversary of Till's birth in 1941. One of the monument sites is the Roberts Temple Church of God in Christ in Chicago, where Till's funeral took place.

The other selected sites are in Mississippi: Graball Landing, close to where Till's body is believed to have been recovered; and Tallahatchie County Second District Courthouse, where two white men who later confessed to Till's killing were acquitted by an all-white jury.

Till, 14 and visiting from Chicago, was beaten, shot and mutilated in Money, Mississippi, on August 28, 1955, four days after a 21-year-old white woman accused him of whistling at her. His body was dumped in a river.

The violent killing put a spotlight on the US civil rights cause after his mother, Mamie Till-Bradley, held an open-casket funeral and a photo of her son's badly disfigured body appeared in Black media.

The national monument designation across 0.02 kilometres squared and three sites marks a forceful new effort by the president to memorialise the country's bloody racial history even as Republicans in some states push limits on how that past is taught.

'Not erasable'

"America is changing, America is making progress," said the Rev. Wheeler Parker Jr., 84, a cousin of Till's who was with the boy on the night he was abducted at gunpoint from the relati ves' house they were staying at in Mississippi.

"I've seen a lot of changes over the years and I try to tell young people that they happen, but they happen very slow," Parker said on Monday in a telephone interview as he traveled from Chicago to Washington to attend the signing ceremony at the White House as one of approximately 60 guests.

Signs erected at Graball Landing since 2008 to commemorate Till's killing have been repeatedly defaced by gunfire.

Now that site and the others will be considered federal property, receiving about $180,000 a year in funding from the National Park Service.

Any future vandalism would be investigated by federal law enforcement rather than local police, according to Patrick Weems, executive director of the Emmett Till Interpretive Center in Sumner, Mississippi.

Other such monuments include the Grand Canyon, Statue of Liberty and the laboratory of inventor Thomas Edison.

"This is an amazing, teachable moment to talk about the importance of this story as an American story that everybody can share in now, particularly at a time when people are trying to rewrite history," said Christopher Benson, president of the non-profit organisation the Emmett Till & Mamie Till-Mobley Institute in Summit, Illinois.

"We have a memorial now that is not erasable. It can't be banned and it can't be censored, and we think that's a very important thing."