Here are the numbers for
cross country in high schools:
Boys -- 231,452
Girls -- 198,199
The link also lists participation numbers for soccer in high schools:
Boys -- 383,824
Girls -- 344,534
US high schools that carry each sport:
Boys XC -- 13,647
Boys soccer -- 11,139
Girls XC -- 13,457
Girls soccer -- 10,548
Ohio only:
Number of schools & participants
Boys XC -- 716...9,654
Boys soccer -- 580...15,610
Girls XC -- 716...8,143
Girls soccer -- 515...13,609
All are taken from an NFHS study. So it appears that soccer does trump cross country in Ohio AND the United States. Soccer is the 5th most participated sport in Ohio for boys high school, cross country is 7th. Soccer is the 5th most participated sport in Ohio for girls high school, cross country is 6th. So cross country is not even close to being the most participated sport in Ohio, let alone the United States -- at the high school level. Here's another
link from NFHS that gives the increases that each sport has had -- soccer is second only to T&F (including both genders), cross country comes in third. And the total numbers actually increase in this other link since it is more recent -- still in favor of soccer.